HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL
Hume and
Dartmouth Dams
Operations Review
Options Paper
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Hume and
Dartmouth Dams
Operations Review
Options Paper
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Please note!
The deadline for
comment on this
paper is Wednesday
10 February 1999
For details see page 1 (‘About this Options Paper’)
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H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
Published by:
Hume and Dartmouth Dams Operations
Review Reference Panel
Postal address:
c/- MDBC, GPO Box 409,
Office location:
c/- Murray-Darling Basin Commission,
Canberra ACT 2601
2nd Floor, 7 Moore Street,
Canberra City,
Australian Capital Territory
Telephone:
(02) 6279 0100;
Facsimile:
(02) 6248 8053;
E-mail:
[email protected]
Website:
http://www.mdbc.gov.au
international + 61 2 6279 0100
international + 61 2 6248 8053
Map on cover: © Copyright Commonwealth of Australia 1985
Remainder of publication: © Copyright Murray-Darling Basin
Commission 1998
This document may be reproduced in whole or in part,
provided that the information in it is not sold for commercial
benefit and its source is acknowledged. Dissemination and
discussion of the document is encouraged. For further
copies and assistance contact the Reference Panel at the
above address.
ISBN 1 875 209 92 1
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Contents
1. About this options paper
3
2. Overview
5
3. Introduction
7
3.1 History of River Murray water regulation
7
3.2 Roles of Hume and Dartmouth storages
7
3.3 The Operations Review
8
3.4 Work related to the review
8
3.5 Community consultation
9
4. Water regulation issues
11
4.1 Identification of issues
11
4.2 Issues that do not involve competing claims for water
11
4.3 Issues that involve competing claims for water
12
5. Issues that do not involve competing claims for water
13
5.1 Economic impact of Dartmouth Dam on the Mitta Mitta valley
13
5.1.1
Effect of Dartmouth Dam on pasture productivity
13
5.1.2
Flood duration in the Mitta Mitta valley
14
5.1.3
Adverse effects on agricultural land at peak regulated flow
16
5.1.4
Erosion on the Mitta Mitta River
16
5.2 Economic impact of Hume Dam on the floodplain below
17
5.2.1
Adverse effects on agricultural land at peak regulated flow
17
5.2.2
The need for a comprehensive river management plan between Hume and Yarrawonga
17
5.3 Effect of dams on non-flow environmental values
19
5.3.1
Impact of Dartmouth Dam on water temperature and quality
19
5.3.2
Effects of regulated flows and rain rejections on natural drying cycles in wetlands
20
5.4 The need to better manage minimum flows downstream of Mildura
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5.5 The need for improved communication
21
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6. Issues that involve competing claims for water
2
23
6.1 Issues and approaches to solving them
23
6.2 Testing single operational changes
24
6.2.1
Natural conditions
26
6.2.2
Benchmark (B42800)
26
6.2.3
Fill and spill (B42810)
26
6.2.4
Provision of airspace (B46770)
27
6.2.5
Relaxed pre-release rules (B42840)
27
6.2.6
Translucent flows (B46750)
28
6.2.7
Use of Dartmouth power station during floods (B42801)
28
6.2.8
“Sharing the Murray” proposal for the Barmah-Millewa forest (B47850)
29
6.2.9
Increased pre-release from Hume Dam (B46160)
30
6.3 Scenarios outside the scope of the review
32
6.4 Combined scenarios
33
7. Summary of options and preliminary panel views
37
Appendix A: Terms of reference for the Operations Review
41
Appendix B: Reference panel
43
Appendix C: Key issues identified in scoping study
45
Appendix D: Details of “Backgrounder” papers
47
Appendix E: Issue register
49
Appendix F: Supporting documents and references
51
Glossary
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1. About this options paper
In December 1996 the Murray-Darling
Basin Ministerial Council agreed that
the way in which Hume and
Dartmouth dams are operated should
be reviewed.
T
he review has been guided by a reference panel
consisting of members representing different
interest groups and drawn from the general
community, and supported by relevant government
agencies.
The Murray-Darling Basin Commission appointed
the reference panel, and the panel’s final product will
be a report and recommendations to the Commission.
However the panel is fully independent and its work
has not been influenced or directed by the
Commission, nor has the Commission considered or
endorsed this options paper.
The technical work has been managed by a small
project team. The team has utilised private
consultants, expertise available in government
agencies and the internal resources of the MurrayDarling Basin Commission. The Commission’s
modelling group has carried out the necessary
computer simulations.
This options paper is the result of the review to
November 1998. It describes the issues that have been
identified as needing attention, the way in which the
panel has gone about its task, the tensions that arise
because of competing objectives for managing the
regulated Murray, and possible improvements and
changes to the balance between competing objectives.
At this stage the panel has reached no fixed
conclusions. The paper presents options, and in most
cases also presents a preliminary panel view.
The work to date now needs to be exposed to the
wider community.
A series of public meetings will be held to present
and explain the material in the paper, discuss the
options, and stimulate comment and feedback. The
panel expects to refine its views in the light of public
comment before making its recommendations to
the Commission.
Comments may be made to any member of the
panel (see contact numbers in appendix B) or can be
addressed to Clarke Ballard, c/o Murray-Darling Basin
Commission, GPO Box 409, Canberra ACT 2601;
telephone 02 6279 0176; fax 02 6230 6005;
email: [email protected]
The deadline for comment is 10 February 1999.
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2. Overview
The terms of reference of the review (see
appendix A) are essentially to review the
operating procedures for the Hume and
Dartmouth Dams and to recommend
how they might be amended to better
address the competing objectives of water
supply, environmental enhancement and
flood mitigation. A broad perspective is
required, including consideration of a
wide range of economic, social and
environmental factors.
T
he reference panel visited many areas of interest
along the river, and spent a lot of time collecting
input from interested groups. The result was a long list
of issues that were seen as important by one or more
interest group. It was necessary to be rigorous in
pursuing only those issues that are related to dam
operation.
Another difficulty in maintaining focus has been the
other processes, programs and inquiries (such as the
Snowy Inquiry and work on environmental flows) that
are under way at present. It has been necessary to
minimise potential duplication and overlap by forming,
as clearly as possible, a picture of the boundaries
between the various activities and where the review fits
into the larger picture.
The panel has found that issues fall into two distinct
groups: those that do not involve finding a balance
between competing claims to water, and those that do.
The first group of issues includes:
• the need for better communication between the
Commission’s operational arm and interested
community groups;
• economic impacts of the dams on human uses of
the floodplains below them;
• management of flow variability in the river
downstream; and
• environmental impacts of the dams (excluding the
impacts of extraction of water further downstream)
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— for example, the fact that water temperatures are
lowered and steady regulated flows diminish
riverbank vegetation and can aggravate erosion.
The panel has been able to arrive at preliminary views
on most of these issues, which tend to be reasonably
self-contained.
The second group of issues essentially revolves
around trade-offs between different management
objectives, and judging where the balance between
them should lie. Computer models were used
extensively to analyse different possible operational
scenarios. These led the panel to a fairly clear
understanding of the effects of each strategy and those
strategies — or packages of strategies — that might be
useful in achieving a different balance. However, no
option was found that resulted in improvements from
the viewpoint of every interest group.
The panel has therefore been unable, so far, to
reach a definitive view on strategies that should be
recommended. Despite this, it has formed a view that
the likely direction is towards a package that includes:
• arrangements for effectively watering the BarmahMillewa forest using the water already allocated for
that purpose,
• continued “harmony” operation of Hume and
Dartmouth storages,
• some form of varied pre-release strategy to mimic
natural variability in flows below the storages, and
• possibly the acquisition of easements over
frequently flooded land between Hume and
Yarrawonga.
Such a package could be implemented with minor
environmental benefits and little adverse effect on
consumptive users, beyond that already in train because
of the water already committed to Barmah-Millewa
watering. However, there would be further environmental
benefits, and further adverse effects on consumptive use,
if pre-release targets were revised to introduce a higherthan-current risk of storages failing to fill.
Floodplain dwellers would obtain some benefit from
these strategies, but those benefits would not
necessarily increase as the specified risk of storages
failing to fill was increased.
The panel seeks opinions from the wider
community on where the balance between the various
competing interests should lie.
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3. Introduction
3.1
History of River Murray water regulation
In its natural state, the Murray was quite different from
the present regulated river. During severe droughts it
was sometimes reduced to a chain of waterholes, but
flows generally followed a yearly cycle. This included
late winter and spring flooding in most years, with high
flows continuing into summer and then gradually
receding until, between February and May, the flow
was reduced in places to a small saline stream. The
Murray was too unreliable in that state to allow its
valley to be intensively settled.
Regulation of the Murray by the construction of
large storages has guaranteed a reliable supply of water,
which has contributed greatly to the development and
prosperity of the region.
Without the Hume Dam (completed in 1936), the
natural River Murray would almost certainly have
ceased to flow in 1939, 1945, 1968 and 1983. Instead, a
flow has been maintained along the river even during
severe droughts. Without this regulation of water flow
much of the development and prosperity of the region
would not have been realised.
The largest economic benefit of the storages has been
a secure supply of water for irrigation and other
purposes. The value of irrigated agricultural production
from the regulated Murray system is in the order of $700
million annually. Many towns and cities, the largest of
which is Adelaide, also depend on the Murray for their
water supply. The regulation of Murray flows has also:
• greatly reduced extremes in salinity levels that
occurred under natural conditions;
• mitigated flooding that would have affected human
activities on the floodplain; and
• enhanced recreational opportunities.
However, regulation has not been without cost:
• valuable land was flooded to provide storages;
• weirs and storages raised and maintained water
levels, causing salinisation and drowning trees;
• wetlands became too wet or too dry;
• diversity of in-stream biota was reduced by release
of cold water;
• more water in summer and less in winter reversed
the natural seasonality of flows;
• natural flow variability and flooding were suppressed;
• red gum forest growth and regeneration were
adversely affected by reduced spring flooding; and
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• erosion was increased by high regulated flows in
some reaches of the river system.
Many of these impacts were unforseen when construction
of major storages commenced. The community has
generally considered that benefits of river regulation
greatly outweigh the costs. With increased knowledge of
impacts caused by our actions, however, community
values have changed. Therefore, the way in which the
Murray is regulated may need to be adjusted to take
account of these changes in community attitudes towards
riverine health.
3.2
Roles of Hume and Dartmouth storages
Hume storage is the primary regulating storage
operated by the Murray-Darling Basin Commission (the
Commission). Hume is drawn down in the summer
and autumn of every year. In contrast, Dartmouth
storage (completed in 1979) is primarily used as a
reserve storage to supplement Hume in dry years or
sequences of years. Dartmouth has a less regular
annual cycle of operation than Hume, and its levels
tend to reflect longer cycles of wet and dry climate. In
the long term it is expected to be full or close to full in
about 30 percent of years, but it may remain below full
for periods of many years.
Although the primary purpose of Hume and
Dartmouth is to store water for consumptive use, they
are also operated to mitigate flooding in the valleys
below them. The two main strategies used to achieve
this are pre-releases and harmony operation.
Pre-releases may be made in the winter or spring if
storage levels and inflows are high and the storage is
certain, or almost certain, to fill. The aim is to delay
filling and so provide additional flood mitigation.
Harmony operation is the transfer of water from
Dartmouth to Hume when the level of Dartmouth is
high. Harmony operation provides more flood
mitigation below Dartmouth Dam and enhances
recreational use of Lake Hume without jeopardising
water supply. Harmony rules are complex, but in
general tend to equalise the chance of spill of the
two storages.
Operational principles and rules are described in
more detail in background papers which were
distributed as the review progressed and can be found in
the support papers (see appendix F).
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3.3
The Operations Review
Against the above background, and because of
suggestions from landholders below the two dams, the
operation of Hume and Dartmouth Dams has been the
subject of a detailed review. This document is the result
to date of the review process.
The Murray-Darling Basin Ministerial Council
defined the terms of reference for the review in
December 1996, as shown in appendix A.
To oversee the review and ensure that all views were
represented, the Commission appointed a reference
panel. Panel members represent various interested
community groups and agencies (see appendix B) and
have been fully involved in all aspects of the project.
The final product of the review will be a report (to be
prepared after further consultation) that the panel will
present to the Commission.
3.4
Work related to the review
To fully address the terms of reference in this review, it
is tempting to expand the review to consider:
• operation of the whole river system;
• water allocations and in-stream flows throughout
the Murray; and
• the impacts of the Snowy Mountains Scheme and
possible changes in its operation, etc.
This would create an immense and unrealistic task and
overlap with work being undertaken by other groups. It
is important to be aware of other work in progress to
make sure that duplication does not occur, but some
overlaps are unavoidable.
The most important and relevant other work
currently under way includes the following:
• Development of River Murray bulk water
entitlements in Victoria, which is well advanced —
including proposals for an enhanced environmental
entitlement for the Barmah-Millewa forest.
• Catchment-by-catchment development of river flow
and water quality objectives, which is under way in New
South Wales but has yet to be applied to the Murray.
• An inquiry into the need for environmental releases
from the Snowy Scheme. The results of this inquiry
have the potential to decrease water passed to the
Murray. Concurrently, relaxation of current fixed
water proportions passed by the Snowy Scheme to
the Murray and Tumut rivers is being examined.
• An Interstate Working Group on River Murray
Flows has been established to develop a River
Murray flow management plan that balances
human and environmental needs. Some work
conducted by the Operations Review — in
particular, the modelling tools developed for the
review — is likely to augment the work of the
Interstate Working Group.
To ensure that the scope of this review was
achievable in an a reasonable time-frame, the review
has concentrated on issues that can actually be
affected by the way in which Hume and Dartmouth
Dams are operated. Figure 1 illustrates the manner in
which the various activities interact.
Figure 1: River Murray Flow Management
Inputs including:
Hume and Dartmouth Dams
Operations Review
Scientific Panel report
NSW water reforms and
environmental flows
Barmah-Millewa forest plan
Victorian bulk entitlement
process
Interstate Working Group
on River Murray Flows:
Stand-alone solutions
from Operations Review
Murray-Darling Basin
Commission
• Community representation
• Agency representation
• Dedicated resources
Snowy Inquiry
Murray-Darling Basin
Ministerial Council
Snowy corporatisation
Future
review
process
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River Murray Flow
Management Plan
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3.5
Community consultation
An essential requirement for conducting the review has
been wide consultation with stakeholders in aspects of
River Murray management defined in the terms of
reference. The broad membership of the reference panel
has been an important part of the consultative process.
Members of the panel have ensured that their interest
groups are informed of review progress. In addition, the
following arrangements were made to ensure that
stakeholders’ interests were fully represented.
• The Australian Research Centre for Water in Society
identified issues that people along the river saw as
important, as the first step in conducting the review.
Identification of these issues was achieved by
telephone interviews with people from a broad
range of interest groups. A summary of the issues
identified is shown in appendix C.
• A series of background papers was produced (see
summaries in appendix D), describing aspects of the
review or present operation. A register of interested
stakeholders was compiled and all background
papers and information about the review were
distributed to these people. The register is constantly
being updated. To add a name to the register, please
call 1800 630 144.
This options paper is the next step in the consultative
process. It is intended to inform people of progress to
date and to gather feedback on the options being
considered. The final step in the review will be the
preparation of a report to the Commission based on
responses to this paper.
The closing date for comment on this paper is
Wednesday 10 February 1999.
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4. Water regulation issues
4.1
Identification of issues
As mentioned earlier, the Australian Research Centre
for Water in Society identified important issues as the
first step in conducting the review. In addition, a
number of interest groups expressed a desire for the
panel to visit their local areas. The panel visited these
areas, discussed issues with local people, and conducted
field inspections in conjunction with scheduled panel
meetings.
Field inspections were conducted in the following areas:
• the Mitta Mitta valley;
• the floodplain between Hume and Yarrawonga;
• municipal areas of Albury and Wodonga;
• (by air) irrigation areas around Deniliquin and the
Barmah-Millewa forest; and
• the Sunraysia area.
Written submissions were also received from:
• interested parties in the Mitta Mitta valley;
• Mitta Mitta Community Action Group;
• Upper North-East River Management Authority;
• River Murray Action Group;
• Corowa caravan parks;
• New South Wales irrigators (Deniliquin area);
• Victorian gravity irrigators; and
• interested parties of the Sunraysia Region of Victoria
and NSW.
An issue register was compiled from these sources
(appendix E), and was progressively updated and
reviewed to identify all issues important to
stakeholders.
The issues were then categorised into two groups:
• issues that do not involve balancing competing
claims, and
• issues that involve balancing competing claims.
Issues that do not involve balancing competing claims are
largely equity-based: they can be remedied by
compensation, engineering works, etc., and do not
require trade-offs between competing claims for water.
An example is the adverse effect of high regulated flow
between Hume and Yarrawonga on agricultural land.
Issues that involve balancing competing claims are concerned
with balancing competing management objectives from
different stakeholders. These issues require analysis by
simulation modelling to compare different operating
strategies. Some of the costs and benefits of each
strategy can be quantified in dollar terms but some,
particularly the environmental ones, cannot. Examples
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of this sort of issue are as follows:
• Provision of space in storages to provide flood
mitigation. This space may decrease reliability of
supply to irrigators and remove environmentally
desirable flooding over the broader floodplain.
• Allowing a percentage of winter and spring inflow
through a storage to reinstate some elements of the
natural flow regime. This policy may be beneficial to
the environment but may reduce reliability of
irrigation supply and increase downstream flooding
of agricultural land.
• A pure “fill and spill” policy maximising supply to
irrigators. This policy provides fewer benefits to
floodplain agriculture and lack of flow variability for
the environment — particularly before spill and
throughout non-spill years.
Issues identified by the review are shown in appendix E
in terms of:
• relevance of issue to each river reach;
• rating of issue according to relevance to the review;
• priority for computer modelling or other assessment
by the review.
The review addressed most issues that have a
medium or higher rating. In many cases, issues with
lower ratings will need to be addressed by other
processes.
The panel has devised options and developed
preliminary views on many issues that do not involve
balancing competing claims for water. They are
included in this paper under each section and the
conclusions. The panel expects to be able to make firm
recommendations to the Commission about most of
these issues.
Firm views have not yet been reached on issues
that do require trade-offs between competing claims for
water. However, options have been narrowed to what
the panel believes are realistic alternatives. The panel
needs wider input on the process by which these
competing claims should be balanced.
4.2
Issues that do not involve competing
claims for water
Major issues that do not involve balancing competing
claims — i.e., issues that do not require balancing of
competing objectives — were identified as:
• Economic impacts of Dartmouth Dam on the Mitta
Mitta valley.
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• Impact of peak regulated flow on agricultural land.
• Lack of comprehensive river management plans.
• Impact of water releases from storages (particularly
Dartmouth) on water temperature and quality.
• Impact of regulated flows and rainfall rejections on
natural drying cycles in wetlands.
• Management of minimum flows downstream of
Mildura.
• The need for improved communication.
These issues are addressed in the following sections
(5.1 to 5.5).
4.3
Issues that involve competing claims
for water
The major issues identified as requiring simulation
modelling were a complex interaction of competing
objectives broadly classified as follows:
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• providing regular and secure water for irrigation,
domestic and industrial consumption;
• mitigating floods below storages to maximise
economic benefits to human floodplain users; and
• making releases in a way that better meets the
needs of the riverine environment.
Due to the complexity of issues that involve balancing
competing claims, computer modelling has been used
to assist in decision making. This modelling has allowed
objective analysis of changes in flow advocated by
stakeholder groups in both dollar and non-dollar terms.
Considerable effort was devoted to developing a model
examining results of operational changes in daily timesteps rather than through traditional models that work
in monthly time-steps. This approach enables closer
examination of benefits and costs of these operational
changes, particularly for flood events.
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5. Issues that do not involve competing claims
for water
5.1
Economic impact of Dartmouth Dam on
the Mitta Mitta valley
There is no doubt that Dartmouth Dam has heavily
modified the hydrologic regime of the Mitta Mitta
valley. The change in flow regime since construction of
Dartmouth Dam has probably been the largest change
experienced anywhere along the River Murray.
The flow regime differs from the natural regime in the
following manner:
• very low flows (less than 500 ML/day) are less
common than under natural conditions;
• flows between 500 and 2500 ML/day are slightly
more common over all, but less common in
summer and autumn;
• flows between 2500 and 6000 ML/day are slightly
less common over all, but significantly more
common in summer and autumn;
• flows between 6000 ML/day and channel capacity
of 10 000 ML/day are significantly more common
— particularly in summer and autumn; and
• flows above channel capacity are less common,
especially at high flood levels, but the duration of
floods that do occur is extended at some levels.
This simple description does not fully represent the impact
that construction of Dartmouth has had on the flow
regime. There are really two river regimes — either of
which may last for many years on end — as follows:
• When Dartmouth is filling (after being drawn down
to supply water for consumptive use), it fully
controls inflow and the valley downstream is almost
entirely flood-free.
• After filling, Dartmouth Storage may remain close
to full for extended periods — being drawn down
under harmony rules in the autumn and refilling,
with pre-releases, in winter and spring. Under this
regime, flood duration may be increased but
frequency is still less than that which occurs under
natural conditions.
Landholders are particularly concerned about the
negative impacts that the dam appears to have exerted
on agricultural profitability. As a result of fewer floods
and lower water tables, pasture growth has been
reduced to the extent that irrigation has become a
necessity. Irrigation can improve production to greater
than pre-Dartmouth levels. However, irrigation
increases operating risks and costs, and requires more
intensive management and capital investment.
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The panel has examined the economic impact of
Dartmouth on agricultural profitability under the
following headings:
• Effect of Dartmouth Dam on pasture productivity.
• Flood duration in the Mitta Mitta valley.
• Adverse effects on small areas of land at peak
regulated flow.
• Erosion on the Mitta Mitta River.
5.1.1
Effect of Dartmouth Dam on pasture
productivity
Independently of the panel’s review, a study of the
effect of Dartmouth Dam on pasture productivity in the
Mitta Mitta valley was commissioned by GoulburnMurray Water and the Commission. This study was
guided by a steering committee consisting mostly of
local landholders and was required to determine:
• the effect of changes in river flow regimes and
subsequent water table levels on productivity of
dryland and irrigated pastures;
• the effect of water temperature on irrigated pasture
productivity; and
• water usage on irrigated pastures and the effects of
water table variation on this usage.
The study found as follows:
• Dartmouth Dam has typically reduced winter/spring
flows, flooding and water table levels.
• Irrigation releases have been irregular in frequency,
timing and duration. However, moderate autumn
releases have been made on a more regular basis
since 1990.
• Soils are highly permeable in general, and water
table levels are often affected by river height,
rainfall, irrigation, run-off and adjacent lagoons.
After rainfall or irrigation, water tables generally fall
within two weeks to a height related to the river
height. Further from the river, groundwater levels
are less clearly related to river height.
• Close to the river (say within 200 m), average
spring water table levels are estimated to be as
much as 1.5 m lower than before Dartmouth Dam
was constructed. Irrigation releases in summer or
autumn result in water table levels as much as 2 m
higher during major releases.
• Dryland pasture productivity is reduced by
Dartmouth Dam where the water table was
previously within 70 cm of the surface —
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particularly during dry spring conditions. Little
effect is felt on dryland pasture productivity where
water table levels were previously deeper than 70
cm. However, productivity during wet seasons is
increased because current water tables are lower
and drainage is better.
• In a well-managed irrigated pasture, there is little
pasture productivity benefit from a higher or
lower water table. With less capable management,
a water table less than 70 cm will improve
productivity.
• Simulations of water releases at 10°C for an entire
irrigation season showed that pasture productivity
would be reduced by up to 15% as a direct result of
application of cold water. This situation represents
the upper limit of the effect of cold water on pasture
productivity, as irrigation releases associated with the
coldest river temperatures would rarely be made for
an entire season. However, colder river temperatures
occur during releases from Dartmouth. Where colder
water releases occur, greater productivity loss than a
10°C scenario may occur.
• Over 40% of diverted water can be lost through
infiltration past the root zone of flood irrigated
pasture, and through channel seepage, evaporation
and run-off. Modelling shows an average annual
irrigation requirement, without losses, of 3.7 ML/ha
to 11.3 ML/ha depending on rainfall. However,
actual irrigation applications are less than those
suggested by the model.
• High and low water table simulations show that
annual irrigation water requirements could be
reduced from 8.5 ML/ha to about 6 ML/ha if a
shallow water table of less than 30 cm were
maintained for the entire irrigation season under
optimal irrigation conditions. If the water table were
maintained at 50 cm, water requirements would
only be reduced to 8.3 ML/ha.
Conclusions derived from these results applicable to
river flow management are as follows:
• More regular summer flows would provide:
– improved pump management,
– reduced pumping costs, and
– reduced irrigation water requirements because
of higher water tables and higher pump flow rates.
• Timing of irrigation releases can have an impact on
dryland and irrigated pasture productivity. Releases
14
H U M E
A N D
from Dartmouth during spring/early summer would
reduce the effects of cold water on irrigation
productivity. These releases would also provide a
higher water table in spring/early summer,
emulating natural regimes and enhancing pasture
productivity.
Landholders believe actions required to remedy
problems highlighted by the report include increased
water allocations and water pricing concessions.
Goulburn-Murray Water, which is responsible for water
licences in the valley, is currently assessing these claims.
To address concerns relating to temperature of
water releases, the issue of a multi-level offtake at
Dartmouth is considered in section 5.3.1.
Based on the results of this study, the panel (noting that
possible increased water allocations and pricing concessions
are currently being assessed by Goulburn-Murray Water
and are now unable to be directly influenced by this
review) has identified the following options:
• Investigate earlier pre-releases in years when
Dartmouth Dam has spilled, to avoid periods of low
flow between spring spills and autumn harmony
releases.
• Investigate lower and earlier releases in years when
resources must be transferred from Dartmouth to
Hume for supply.
The panel’s preliminary views are as follows:
• Goulburn-Murray Water is dealing adequately with
possible increased water allocations (in the context
of the Murray-Darling Basin Commission Cap),
pricing concessions and any other compensation
measures for adverse effects on individuals.
• Current harmony rules provide for releases as soon
as practicable following Hume ceasing to spill, and
this provision should be retained.
• When Dartmouth releases are needed for supply
purposes, there may be some scope for earlier
releases at lower rates; however, this could involve
increased risk of loss of water for consumption.
5.1.2
Flood duration in the Mitta Mitta valley
It is well understood that Dartmouth markedly reduces
the frequency of flooding in the valley below —
virtually eliminating flooding for long periods when the
storage does not spill. However, there has been much
D A R T M O U T H
D A M S
O P E R A T I O N S
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Table 1: Modification of flood regime at Tallandoon since construction of Dartmouth Dam
Flow at
Average no of floods/year
Average flood duration (days)
Average days flooded/year
Tallandoon
Pre
Post
%
Pre
Post
%
Pre
Post
%
ML/day
Dam
Dam
change
Dam
Dam
change
Dam
Dam
change
10 000 (channel
3.59
1.78
-50
7.2
6.3
-12
25.8
11.2
-57
13 000
2.75
0.87
-68
5.3
6.3
+19
14.4
5.5
-62
19 000
1.49
0.33
-78
3.5
4.6
+31
5.2
1.5
-71
0.62
0.16
-74
2.8
2.0
-29
1.7
0.3
-82
capacity)
(minor flooding)
27 000
(moderate
flooding)
discussion about the effect of the dam on duration of
floods occurring when the storage is full.
Some landholders state that before Dartmouth was
constructed “floods never lasted longer than a few days,
and were beneficial”. However, in a survey conducted
during early stages of dam construction, beef and dairy
farmers listed fear of catastrophic floods as a major
barrier to farm development.
To objectively assess the impact of the dam on
flooding, the flood frequencies and durations under
pre-Dartmouth and post-Dartmouth conditions were
compared using computer simulation models (see
section 6 for a description of the models and the
support papers for a detailed report on Mitta Mitta
flood duration).
Modification of the flood regime by Dartmouth
Dam at Tallandoon is summarised in table 1.
This table shows that Dartmouth Dam removes
about half the low-level floods and three-quarters of
higher level floods. It also reduces average flood days
per year by a similar proportion. At some levels,
duration is increased for floods that are not removed; at
other levels, average duration is decreased.
At the nominal river channel capacity at Tallandoon
(10 000 ML/day), average flood duration is somewhat
decreased. However, some floods at that level are
extended in duration by the storage. This effect is
particularly apparent for floods that occur when the
storage is already full.
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
The panel has reached the conclusion that the dam has
a powerful effect in reducing both frequency and peaks
of floods in the Mitta Mitta valley. As discussed in
section 5.1.1, this reduction in frequency and peaks
provides both advantages and disadvantages to
agricultural productivity.
While it is true that some floods are extended in
duration (at the 10 000 ML/day level at Tallandoon), it
is equally true that some are decreased in duration. Over
the 63 years modelled, there were 13 such floods that:
• lasted more than ten days under both the preDartmouth and post-Dartmouth scenarios, and
• were individual floods that could be directly compared.
Comparison of those floods showed that the dam could
extend flood duration by as much as eight days, but
conversely could reduce it by as much as eight days. The
average effect was an increase in duration of 2.4 days.
Stakeholders have expressed some concern that the
dam sometimes increases the duration of floods at
particular levels, despite the powerful overall flood
mitigation effect. The review panel believes that it is
possible to change storage operation so that duration
above nominal channel capacity at Tallandoon is not
increased. However, this change would cause increased
flood peaks.
This option and the views of the panel are discussed
further in section 6.2.7 (‘Use of Dartmouth power
station during floods’). In summary, however, the panel
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considers that initially the question of using the power
station to assist in controlling flood duration is a matter
for the Mitta Mitta community to reach an agreed
position on.
5.1.3
Adverse effects on agricultural land at
peak regulated flow
The nominal channel capacity of the Mitta Mitta River
for regulated releases has been set at 10 000 ML/day.
In 1984, several regulators were installed with
Commission funds on lagoons and anabranches
alongside the lower reaches of the river. These
regulators were intended to prevent high regulated
flows from backing out on to the floodplain.
Unfortunately, the regulators were generally
unsuccessful because of construction problems and
permeable soils allowing lagoon levels to vary with
river levels. Waterlogging, as distinct from inundation,
also occurs on a number of properties in this area.
During 1997–98, slightly lower (9500 ML/day)
regulated releases were trialled. The lower releases
resulted in the affected area being reduced. However, at
least two properties were still affected by waterlogging
and/or inundation.
The panel considers that there are three options for
resolving this problem:
• investigate nominal channel capacities in the range
9000 to 10 000 ML/day;
• investigate construction of regulators where
appropriate; or
• take flood easements over affected land and pay
appropriate compensation.
The panel has further considered these options in light
of the following factors:
• problems may be minimised by carefully selecting
the regulated release figure;
• regulators may only be required on one or two
properties; and
• easements could be taken over the affected land if
no structural solution is possible.
It is the view of the panel that further investigations
should be conducted to ascertain the most beneficial
option for each affected property.
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5.1.4
Erosion on the Mitta Mitta River
The Mitta Mitta stream and floodplain are relatively
steep and there are few geomorphic controls — such as
bedrock bars — that limit on-going fluvial geomorphic
processes. Erosion was prevalent on the river prior to
construction of Dartmouth Dam. In 1955, almost 25
years before completion of the dam, the Mitta Mitta
River Improvement Trust was formed to manage the
erosion problems.
When Dartmouth Dam was constructed, possible
adverse effects on river stability were anticipated. The
Commission has therefore contributed to erosion
control work. This work is now conducted by the North
East Catchment Management Authority (NECMA).
Most erosion work conducted since formation of the
Mitta Mitta River Improvement Trust has used willows
and selective rock beaching as the primary control
method. This approach has led to two problems:
• expensive control measures for excessive willow
growth, and
• lowered environmental values caused by gradual
conversion of the stream to a rock and willow lined
channel.
In a submission to the review, the Upper North East
River Management Authority (the predecessor of
NECMA) stated that division of responsibilities between
it, Goulburn-Murray Water and the Commission were
unclear. Accordingly, the authority identified a need to:
• formalise management roles,
• resolve management requirements, and
• clarify funding arrangements.
The submission also suggested that an integrated program
of waterway and floodplain management should be
developed for the Mitta Mitta River. It recommended that
this program should include plans for:
• Floodplain management — including pasture, flood
and drought management.
• Stream health — including stream geomorphology
and stability, riparian vegetation and habitat, instream ecological conditions, and water quality.
• Stream operational requirements — such as release
rates, drawdown rates, and community awareness
provisions.
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Based on the submissions received and analysis
conducted by the panel, the following options have
been identified:
• Continue with existing stream erosion control
methods, accepting that the result over time will be
a willow and rock lined river channel of limited
environmental value.
• Fund further research into mechanisms and factors
contributing to slumping of banks on the Mitta
Mitta River.
• Develop an integrated program of waterway and
floodplain management along the lines suggested by
the NECMA.
The panel’s preliminary view is that an integrated
program of waterway and floodplain management
along the lines suggested by the NECMA should be
developed.
5.2
Adverse effects on agricultural land at
peak regulated flow
Channel capacity of the Murray between Hume and
Yarrawonga has been regarded for many years as
25 000 ML/day at Albury. Although nominal channel
capacity — and therefore peak regulated release from
Hume — have not changed, regulated diversions from
the system have increased steadily over the past three
decades leading to longer periods of high regulated flow.
This part of the Murray is not a single river, but rather
a main stream with many anabranches (refer to back
cover). In some places the anabranches carry more flow
than the main stream During the late 1970s, regulated
flows of increasing magnitude led to concerns that access
to islands of freehold land was being cut off by
anabranches. In particular, many formerly intermittent
anabranches started to run throughout the irrigation
season. Many of these problems have been resolved by
establishing a program in which the Commission
contributed to the cost of access bridges or acquiring
easements where provision of access was not justified.
Another problem, however, is emerging. Areas of
freehold land on some properties are being inundated
at peak regulated flow, or are being waterlogged,
because the land is marginally above river level and lies
above sand/gravel lenses connected to the river.
H U M E
The panel considers the options for dealing with this
problem are to:
• reduce peak regulated flow level to a figure
significantly lower than 25 000 ML/day;
• do nothing, on the basis that the negative impacts
are outweighed by flood mitigation benefits to
agricultural land; or
• take flood easements over the affected land and pay
appropriate compensation.
Economic impact of Hume Dam on the
floodplain below
5.2.1
Sometimes it takes days or weeks of high regulated flow
before waterlogging occurs. Affected areas can be identified
by changes in vegetation — typically weeds replacing
paspalum — even in the absence of visible waterlogging.
As part of the review, Hassall & Associates inspected
most of these areas in December 1997 to assess the spatial
extent and cost of mitigating the effects of this waterlogging.
They found that about 250 to 300 ha was affected, and
estimated the value of the affected land at about $375 000.
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
It is the view of the panel that, for equity reasons, taking
flood easements over the affected land and paying
appropriate compensation is the only reasonable option.
5.2.2
The need for a comprehensive river
management plan between Hume and
Yarrawonga
River regulation and flow regimes
Regulation of the River Murray between Hume and
Yarrawonga has progressively increased since
construction of the original Hume Dam in the 1920s.
Since then, the Snowy Mountains Scheme has been
built, capacity of Hume has been doubled, and
Dartmouth Dam has been constructed. Irrigation
development has matched the increased storage
available, and the flow regime is now very different
from the natural regime, in that:
• Low flows (1200 – 5000 ML/day) are more common
— particularly in winter and early spring as storages fill.
• Flows between 15 000 and 25 000 ML/day are more
common — particularly in summer and autumn
when natural flows would be lower. In most years,
there are now extended periods of flow close to
25 000 ML/day during the irrigation season. Prerelease of water at this rate, to mitigate potential
flooding in winter and spring, is also quite common.
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Table 2: Effect of Snowy and Murray River development on floods below Hume
Flow at
Albury
Average no of floods/year
Natural
Present
ML/day
25 000 (channel
Average flood duration (days)
%
Natural
Present
change
Average days flooded/year
%
Natural
Present
change
%
change
4.37
2.10
-52
13.27
14.88
+12
57.99
31.25
-46
31 500
4.25
1.51
-64
9.52
13.60
+43
40.46
20.02
-51
36 000
3.79
1.35
-64
8.33
12.00
+44
31.57
16.20
-49
0.62
0.16
-74
2.8
2.0
-29
1.7
11.20
-49
capacity)
(minimal
flooding)
43 000
(minor flooding)
• Flows significantly above 25 000 ML/day are less
common because of the flood-mitigating effect of
the storages. However, the duration of low-level
flooding can be extended at times.
• Seasonality of river flows has changed markedly.
Much higher flows are experienced in summer and
autumn, and lower flows in winter and spring.
• Total water volume is about 6% more than under
natural conditions as a result of water diverted from
the Snowy catchment.
Effects of water storages and the Snowy Mountains
Hydro-electric Scheme on River Murray floods below
Hume have been quite significant. Table 2 illustrates
changes in flooding as a result of these water control
structures.
The table compares natural and present-day
frequency, duration and total annual days flooding at
various flow levels. Figures are for events exceeding
one day’s duration occurring from June to December
inclusive.
•
•
•
River regulation and erosion
Between Hume and Yarrawonga, erosion is more active
than in other reaches of the River Murray. Consultants
Ian Drummond and Associates (1993 and 1997)
investigated the nature and extent of channel
instabilities in the reach. They concluded as follows:
• The river channel has deepened between Hume
Dam and Albury, and has become shallower
18
H U M E
A N D
•
downstream of Howlong. There has been little
change in depth between those locations. The depth
throughout the Hume-Yarrawonga reach is now
fairly stable and the bed has become armoured by a
coarse layer of gravel.
The river has historically moved over the floodplain
by a process of lateral migration of bends. This
migration is occurring at present, but it is not clear
whether or not the regulated flow regime has
affected the rate of migration of bends.
In contrast, there is a clear link between river
regulation and general channel widening. River
regulation, in conjunction with other land
management practices, has led to a general
widening of the river channel of about 160 mm per
year. It is likely that river regulation has been a
major contributor to depleting the incidence and
extent of vegetation on the river bank. The long
periods under regulated flow soften the banks and
lead to higher rates of bank erosion.
Banks are generally retreating in a parallel fashion
— notch erosion at high regulated flow level is not
the main mechanism. Erosion is occurring across
the full height of the bank.
Anabranches carry large volumes of water under
regulated conditions. In one location, the main
stream carries less than half the peak regulated flow.
Anabranches need to be examined individually to
assess changes and the possibility of capture of the
main river channel.
D A R T M O U T H
D A M S
O P E R A T I O N S
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H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
• Regulation of flows causes a higher proportion of
flow to pass along the river channel and less along
the floodplain. It is estimated that re-regulation
within Hume increases the energy within the river
channel (hence potential erosive power) by about
6%. Re-introduction of elements of the natural flow
regime, combined with other management tools,
may help to control channel erosion.
• Erosion rates are high during floods, but the majority
of erosion is occurring from flows within the
channel. The flows within the channel are mostly
irrigation releases, but also include flood pre-releases.
• It is not possible to quantify the relative effects of
irrigation releases, flood releases and Snowy
diversions on channel erosion in the reach.
• Factors such as de-snagging (which tends to increase
both channel capacity and erosion rates), changes in
vegetation (partly but not solely because of increased
regulation) and boating (probably quite limited) also
contribute to changed rates of channel erosion.
The panel accepts that flow regulation has had a major
influence on channel stability in the Hume-toYarrawonga reach of the Murray. However, the panel is
also aware that the river has historically migrated
around the floodplain. This fact is obvious from aerial
photographs or maps of the area — including the map
on the cover of this paper.
• a decision on the extent to which anabranch
development needs to be contained;
• setting desired levels of protection for aquatic,
riparian and floodplain habitats; and
• documenting desired aesthetic and recreational values.
Based on the strategic framework, a comprehensive
river management program should be developed. This
program would:
• establish an agreed management arrangement
(which needs to work in two states, have proper
local input, etc);
• establish links with associated land management
programs in each state;
• establish agreed funding arrangements — with
consideration of funding from such sources as the
Commission, catchment management authorities
and local government, and input (cash or kind)
from landholders;
• set a works program — including both an annual
program of necessary patch-up works (done now to
a modest extent with Commission funding) and a
coordinated strategy of activities designed to achieve
the long-term goals; and
• monitor progress and the extent to which the
strategic framework might need to be changed.
The panel considers that future options for
management of this reach of the Murray are to:
• retain the present management arrangement — under
which the Commission provides limited funding to the
NSW Department of Land and Water Conservation to
treat actively eroding sites on a priority basis; or
• develop a comprehensive and properly funded
program for management of the reach.
5.3.1
The panel believes that this issue can only be fully
addressed by developing a comprehensive and properly
funded program for management of the reach. The
management program will initially need a strategic
approach to articulate a vision for the future desirable
state of the river. The strategic framework will require:
• developing criteria for acceptable and unacceptable
erosion rates (& acceptable methods of erosion control);
• setting limits to acceptable rates of channel
widening and bed degradation;
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
5.3
Effect of dams on non-flow
environmental values
Impact of Dartmouth Dam on water
temperature and quality
Water from Dartmouth Dam is normally released through
the high-level outlet, except when storage content drops
below about 30% and the low-level outlet must be used.
The high-level outlet draws water from about 60 m
below the full supply level of the storage.
The temperature of water from the high-level outlet
is considerably lower than river temperature prior to
construction of the dam — particularly in summer and
autumn. Water quality of releases from the high-level
outlet is also lower than water near the surface. The
low-level outlet exhibits similar, but amplified, water
quality and temperature problems. Releases of lowtemperature water and/or poor quality water from
these outlets may be responsible for:
• declining habitat and native fish population in the
river (temperature is identified as the critical factor);
and
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• landholders being unable to achieve the full
potential of pasture productivity improvements by
irrigation partly because of low water temperatures
— see section 5.1.1 (‘Effect of Dartmouth Dam on
pasture productivity’).
During construction of the dam, provision was made in
the existing high-level-outlet offtake tower for future
extension above full supply level if required. It has been
provisionally estimated that the extended tower with
multi-level offtakes would increase temperatures
significantly and improve other water quality factors.
However, it is highly unlikely that the extended tower
would restore temperatures and water quality to
natural pre-dam levels. A feasibility stage cost estimate
of the extension is $11 million.
An alternative to the tower extension would be to
add shutters to the existing tower, which would be much
cheaper. These shutters would vary draw-off levels to a
limited extent, but would provide little improvement in
water temperature or quality over the current situation.
In assessing the benefits of extension or
modification of the existing high-level outlet, the panel
considered the following issues to be important:
• Likely temperature increases will probably not
restore pre-Dartmouth conditions to the extent that
suitable spawning habitat for all native fish will
return. Conditions may well be favourable for
Murray Cod and Macquarie Perch but not for some
other species. This needs to be investigated.
• The dam itself will remain a barrier to fish
migration.
• Water quality from the low-level outlet will not be
improved. The low-level outlet was used in 1983 and
briefly during the early 1990s, so its historic frequency
of use is low. However, the storage can remain low for
years on end: in the long term it is estimated that it will
be used 15% of the time. Water quality from this outlet
is potentially poor, with low dissolved oxygen levels
and considerable dissolved iron, manganese and
hydrogen sulphide.
Based on submissions received and analysis conducted
by the panel, the following options have been
identified:
• No action — accept that temperatures in the Mitta
Mitta River will remain depressed, and that the river
ecology will remain altered from its natural state.
20
H U M E
A N D
• Install shutters on the existing high-level outlet to
provide limited improvement.
• Raise the top of the existing structure to above full
supply level and install a fully functional multi-level
offtake.
• Agree in principle that a fully functional offtake is
required, and conduct detailed investigations into
the cost, benefit and optimum way to achieve a
fully functional offtake.
The panel’s preliminary view is that it agrees in
principle with the last option: that a fully functional
offtake is required and that detailed investigations into
the cost, benefit and optimum way to achieve a fully
functional offtake must be undertaken.
5.3.2
Effects of regulated flows and rain
rejections on natural drying cycles
in wetlands
Too much flooding can be as damaging to a naturally
ephemeral wetland as insufficient flooding. Many
plants need a wetting and drying cycle for their seeds to
germinate and their roots to be aerated. Drying also
permits oxygenation of sediments — a crucial step in
the process of nutrient cycling — which in turn
supports aquatic food webs.
Some wetlands along the Murray are inundated at
peak summer regulated flow. Others are not, but can be
affected when summer rain causes rain-rejection of
irrigation water which is returned to, or left in, the river.
The panel considers that this issue will require
considerably more work, integrated into river flow
management plans, and that solutions are likely to
involve the following:
• Improved river operation. Improved river operation
may be possible from better weather forecasts, more
accurate ordering from irrigation agencies, and
improved estimation of river losses.
• Retention of rain rejections in storage of some kind. Four
possibilities have been identified, as follows:
– storage on-farm, particularly as drainage
recycling dams become more popular;
– storage in distribution channels;
– continued emphasis on drainage diversion
permits to encourage irrigators to pump from
authority drains, which contain a proportion of
D A R T M O U T H
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O P E R A T I O N S
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rain rejection water; and
– provision of storage airspace in some weir pools.
• Physical works on individual wetlands. Works
would consist of banks, regulating structures and
perhaps pumps to control the extent to which water
was introduced into, or kept out of, a particular
wetland at different times of the year.
Again the panel considers that it is likely that the
Interstate Working Group on River Murray Flows will
need to consider this issue in some detail.
5.4
The need to better manage minimum
flows downstream of Mildura
When demand downstream of the Darling–Murray
junction is supplied from the Darling, flows at Mildura
can be quite low. Current Commission operating
procedure is to pass a minimum flow at Euston Weir of
2450 ML/day plus expected diversions at Red Cliffs,
FMIT, Merbein, Coomealla, Curlwaa and Millewa
pump stations. This flow suggests that 2450 ML/day
covers private diversions between Euston and Mildura
Weir, river losses in that stretch, and the flow past
Mildura Weir.
There are operational difficulties in accurately
maintaining this small flow at the end of a long river
system with little re-regulating capacity. On occasions,
the flow at Mildura is less than planned, which
increases salinity levels and promotes the growth of
algae in Mildura Weir Pool.
The panel considers that there are three options for
resolving this problem as follows:
• Obtain more precise orders from diverters. Orders
for major diversion points (Red Cliffs etc.) are
received a week in advance, but are not always
adhered to. Private diverters are relatively
uncontrolled.
• Utilise more storage volume in weir pools. Most
weir pools are operated at almost constant levels,
which is convenient for water diverters and boating
interests but provides little or no scope to reregulate water. The constant pool levels also have
environmental disadvantages.
The exception is Euston Weir pool, which has
an official operating range of 1.2 m (20 000 ML)
below full. In fact it can be drawn down further: as
far as 2 metres in an emergency. However, this
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
capacity is not often used, because boating interests
tend to object, and the normal operating range is
only 0.3 metres below full. There is scope for more
variation in operating levels, subject to local
agreement.
Potential gains in operational flexibility by allowing
Mildura Weir levels to fluctuate are much smaller than
at Euston. However, there are likely to be
environmental benefits in introducing some variation.
• Improve measurement. Measurement points are
presently at Euston and Wentworth, with no reliable
measurement at Mildura. Mildura flows can be
calculated from the Wentworth measurement,
allowing for Darling inflows and changes in weir level.
Considerable improvements in flow control could be
achieved by improved measurement at Mildura. The
most feasible measurement improvement would
probably be to reduce or quantify leakage at the weir
and measure the flow over it.
It is the view of the panel that all three options can be
adopted. This issue is essentially one of better flow
control in this reach of river. Operation of Hume and
Dartmouth Dams has no direct effect on control of
these flows; the problem needs to be solved in the
context of flow management of the whole river.
5.5
The need for improved communication
The need for better communication between the
Commission (in its role as river operator) and
communities along the river was identified as a
significant issue during the initial stages of the review.
This perception of poor communication was evident
to the panel in various locations. To some extent it
contrasts with the Commission’s good reputation for
producing excellent publications and educational
material that target the general public.
The panel formed the view that operation of the
river system is not well understood, and this may be
part of the problem. Regular communication between
interested groups and the actual river operators is
required — not a spokesperson or public relations
person. It is recognised that, technically, the customers
of the Commission (or the newly formed River Murray
Water) are the states, and that within-state operating
agencies have the primary contact with retail
customers. That is beside the point. The public
R E V I E W
21
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
perception is that the Commission operates the river, so
the Commission is blamed if the operation is seen
(fairly or unfairly) to be inadequate.
Within-state operating agencies have well
developed communication channels with water users,
but not with recreational or tourism interests, or with
floodplain users who are not irrigators. This is where
better communication is needed.
The nature of the communication needed would
vary between groups. For example, landholder groups
along the Mitta Mitta and between Hume and
Yarrawonga have a keen interest in storage operation.
Therefore, they require regular meetings — perhaps
with extra communication as storages get close to full.
Other groups may need less frequent liaison. For
example, there is a need to provide the general
community, and developers, with a better
understanding of flow and storage level variation,
system operation and actual flood risks, so that
development decisions are based on a realistic
22
H U M E
A N D
knowledge of the likely risk factors. This level of
communication should also be planned and continual,
but need not be as frequent as is needed with those
interested in actual storage operation.
The communication arrangements must be
integrated with other processes such as work of the
Interstate Working Group for River Murray Flows and
the development of comprehensive river management
plans. There is a need for some sort of broad based
reference group to advise on communication needs.
The panel has concluded that formal and continuous
liaison should be set up between the Commission (or
River Murray Water) and interested community
groups. This liaison should be:
• regarded as a permanent commitment — not just
something to be fitted in when time is available; and
• of a frequency and form negotiated with particular
interest groups to suit their needs.
D A R T M O U T H
D A M S
O P E R A T I O N S
R E V I E W
6. Issues that involve competing claims for water.
6.1
Issues and approaches to solving them
As already indicated, some issues amount to tensions
between competing interests or management objectives.
Examples of different stakeholder groups’ conflicting
objectives are as follows:
Irrigators desire a consumptive yield as high and
secure as possible. This implies few spills of water and a
high degree of flow control. However, the Ministerial
Cap on water diversions means that average
consumption of water cannot increase above
benchmark levels. Irrigators seek to maintain the
existing water security and water availability on which
their business depends.
Floodplain landholders want to have as much flood
protection as possible to agricultural land on floodplains
below the storages — except for the Hume-Yarrawonga
reach, where they may be interested in allowing
frequency of flooding of low-lying land to be increased
if better protection can be provided for higher (but still
flood-prone) land.
Environmentalists (and all other stakeholders to
varying extents) are interested in improving the
ecological health of the river system. Predictive
relationships are not usually available to demonstrate
what flow is required to maintain a particular
percentage of habitat, species abundance or diversity of
species. In general, any change that tends to return the
system to its natural (pre-dam) state is seen as moving
in the right direction, and any change in the opposite
direction is seen as detrimental.
Hydro-electric power station operators want to
maximise the economic value of the electrical energy
they generate. This is partly a function of:
• maximising water volume passed through the
power station,
• available head, and
• being able to generate when spot prices for energy
are highest.
Recreation and tourism interests have diverse
needs, including the following:
• Users of Lake Hume want its level kept up — a
target of 50% capacity until after Easter is quoted.
• Caravan park owners below Hume must evacuate
parks at about 4.3 metres gauge height at Albury, so
they want floods above this level to be minimised.
• Providers of tourist accommodation want a healthy
river because the river is the main attraction for
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
their customers. However, they dislike the adverse
publicity that can come with large floods.
• Boat operators want certainty and, generally, as
little variation in river levels as possible.
• Recreational fishing interests and ecotourism
operators want a healthy river.
Many aspects of these competing interests can be
quantified, or at least clarified, by simulation modelling.
Consequently, the review panel has put considerable
effort into developing suitable computer models to
support decision making.
Computer modelling
Computer modelling of water supply systems simulates
(as closely as possible) the operation of the water
supply system under any scenario or given set of
conditions, through the historic sequence of climate for
which information is available. In this case:
• The system is the River Murray and its storages
(Dartmouth, Hume, weirs along the Murray, Lake
Victoria, and Menindee lakes). It is necessary to
include the whole system because it is operated in
an integrated way.
• The conditions that can be specified include:
– level of irrigation demand;
– size of storages;
– detailed operating rules for the storages; and
– any changes in inputs to the system (for
example, returning water to the Snowy River,
which would decrease flows into the system).
• Each scenario (or simulated option) operates the
system under a fully described set of conditions to
see what would have happened through the historic
sequence. The results are available in whatever
format and degree of detail is required, allowing
different scenarios to be compared.
• The historic sequence for which information is available
is the period for which the necessary data (inflows,
temperature, evaporation, rainfall) are available.
Two existing Commission models were linked to
produce the model used in this review:
• The Monthly Simulation Model (MSM) — a welldeveloped and robust model that operates in
monthly time-steps. This model is satisfactory for
resource management purposes, but does not
provide the level of detail needed to look at possible
changes to flood operation.
R E V I E W
23
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
Table 3: Comparison of selected scenarios
• BIGMOD — a daily model that provides detail for
the part of the water supply system upstream of
Yarrawonga. Essentially, BIGMOD takes MSM
output and reprocesses it in daily time-steps to
produce daily output for that part of the system.
The daily output is used to estimate costs to
floodplain landholders of flooding below the
storages. It is also useful for looking at in-stream
variation from the environmental viewpoint.
6.2
Testing single operational changes
In total, more than 30 scenarios were modelled to
explore the effects of possible changes in operations.
Full details are available in a support paper, ‘Details of
simulation runs’, which contains a full set of outputs,
and a description of output parameters and options
modelled.
It is tempting to combine what appear to be
promising ideas into packages of proposals early in the
investigation when modelling a large number of
scenarios. This tendency can quickly lead to the volume
of models and results getting out of hand. Consequently,
the panel decided that only single changes to benchmark
conditions would be modelled as a first step. Only when
all single-change options were complete were a number
of carefully selected combinations examined.
Representative examples of single-change options
modelled by the panel are as follows (numbers in brackets
refer to the run modelled under a particular scenario):
•
•
•
•
•
•
•
Natural conditions
Benchmark run (B42800)
Fill and spill (B42810)
Provision of airspace (B46770)
Relaxed pre-release rules (B42840)
Translucent flows (B46750)
Use of Dartmouth power station
during floods (B42801)
• Proposal to water the
Barmah-Millewa forest (B47850)
• Increase allowable pre-releases
from Hume (B46160)
Section
6.2.1
6.2.2
6.2.3
6.2.4
6.2.5
6.2.6
6.2.7
6.2.8
6.2.9
The following sections describe the main features of the
modelling and discuss the results of the scenarios
above. The results are also summarised in table 3.
24
Run Number
Natural
Conditions
Run description
DOLLAR
Absolute
FLOODING (1934-1997)
Mitta Mitta at Tallandoon
Floods/year
Average days flooded/year
Average flood costs/year ($000)
Murray at Albury
Floods/year
Average days flooded/year
Average flood costs/year ($000)
Murray at Tocumwal
Floods/year
Average days flooded/year
Average flood costs/year ($000)
IRRIGATION (1891-1997)
New South Wales
Average diversions (GL)
Maximum shortfall (GL)
Average production value ($000/year)
Victoria
Average diversions (GL)
Maximum shortfall (GL)
Average production value ($000/year)
South Australia
Maximum shortfall (GL)
HYDRO ELECTRIC GENERATION
Dartmouth (1934-1997)
Average volume spilled (GL/year)
Average power generated (Gwh/year)
Value of power generated ($000/year)
Hume (1891-1997)
Value of power generated($000/year)
SUMMARY OF DOLLAR IMPACTS ($000/yr)
Irrigation (1891-1997) NSW+Vic
Hydro electricity
Salinity
Flooding (1934-1997)
Hume recreation (1891-1997)
Total dollar benefit ($000/year)
1.21
19
506
1.38
48
2394
1.02
23
1358
0
0
0
0
0
0
0
0
0
0
0
0
-4 258
0
-
NON DOLLAR
Absolute
DARTMOUTH TO HUME REACH
Floodplain inundation (1+ day floods Jun-Dec)
No. years with an event > 13 000 ML/day
No. years with an event > 19 000 ML/day
Channel stability
Average annual flow within river banks (GL)
1 153
HUME TO YARRAWONGA REACH
Floodplain inundation (1+ day floods Jun-Dec)
No. years with an event > 25 000 ML/day
No. years with an event > 31 500 ML/day
Channel stability Average annual flow within river banks (GL)
57
52
4 016
BELOW YARRAWONGA
Floodplain inundation (7+ day floods Aug-Jan)
No. years with an event > 14 000 ML/day
No. years with an event > 25 000 ML/day
Channel stability Average annual flow within river banks (GL)
Bird & fish breeding indicators (over 106 yrs)
No of "excellent" years
No of "good" years
Barmah Forest watering indicators (106 yrs)
Years with 1 month or more > 550 GL (Yarra)
Years with 1 month or more > 912 GL (Yarra)
Years with 1 month or more > 1039 GL (Yarra)
Hattah Lakes watering indicators (106 yrs)
Yrs 1 month or more > 1116 GL (flow to lakes)
Yrs 1 month or more > 1487 GL (good floods)
43
36
61
53
3 378
45
24
98
73
68
93
72
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
B42800
Benchmark
B42810
Fill and
spill
IMPACTS
B46770
Allow 200
GL airspace
in Dart. and
300 GL
in Hume
June-Oct.
B42840
Pre-release
based on
minimum
irrigation
demands
B45770
Hume &
Dart. 30%
translucent
June-Sept.
B46750
Hume &
Dart. 30%
translucent
June-Sept.
Translucency
turned off if
dams<60% full
B42801
Use
Dartmouth
power
station
during
floods
B46160
Increase
allowable
Hume prereleases to
31500
ML/day
B46950
Sharing
the Murray
Barmah
/Millewa
proposal
DOLLAR IMPACTS
Absolute
Difference (this run minus Benchmark)
0.37
12
244
0.18
5
68
-0.05
-1
-61
-0.02
-2
-55
0.11
2
5
0.08
0
-12
0.16
0
56
0.00
-0
-0
0.02
-0
5
0.70
26
1133
0.05
0
86
-0.16
-4
-220
-0.17
-5
-234
-0.06
-4
-193
-0.03
-2
-125
0.02
-0
7
0.05
4
3
-0.01
-0
17
0.54
13
654
0.02
-0
48
-0.02
-0
-108
-0.08
-2
-115
0.03
-0
-60
0.03
-0
-69
0.00
0
10
0.03
0
1
0.00
0
10
1 888
2 518
222 478
6
-0
599
-20
-3
-1 829
-9
-4
-840
-69
-87
-6 431
-13
-3
-1 218
0
0
0
-0
0
-87
-18
-81
-1 570
1 624
841
329 327
0
0
9
-4
0
-197
-0
0
-28
-15
39
-722
-0
0
-23
0
0
0
-0
0
-12
-8
0
-219
396
1
0
-0
57
1
0
0
16
97
263
4 254
44
-17
-63
-27
5
176
-21
8
120
-10
-8
-51
-10
1
78
-85
32
476
-2
0
7
2
6
68
3 989
-163
-42
15
-97
-0
0
-13
-40
551 804
8 243
-66 633
-2 031
2 184
493 568
609
-227
-101
-202
-74
4
-2 026
134
505
388
-81
-1 080
-868
135
29
404
-26
-326
-7 153
-148
285
248
-127
-6 895
-1 241
78
332
206
-26
-651
0
476
0
-74
0
402
-98
-6
-134
-3
-2
-244
-1 789
29
427
-33
-36
-1 403
IMPACTS
NON DOLLAR IMPACTS
Absolute
Difference (this run minus Benchmark)
18
9
2
2
-1
-2
-1
-1
3
3
1
1
1
0
0
0
1
1
1 244
-23
9
9
-4
-0
-9
0
0
42
27
5 070
2
0
-52
-4
-4
92
0
-2
110
2
1
64
-2
0
47
0
0
-3
2
0
-16
0
0
5
57
36
3 475
1
0
-9
4
-1
35
1
0
24
2
2
31
0
0
19
0
0
-0
0
0
-0
4
-1
38
9
20
0
-1
0
-4
0
-3
0
-4
0
-2
0
0
0
-1
29
-16
55
37
29
0
-2
1
0
-2
0
1
-1
2
7
1
4
2
-2
1
0
0
0
0
0
0
2
-1
2
45
33
0
-1
0
0
0
1
2
2
0
0
0
0
0
0
0
0
25
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
6.2.1
Natural conditions
6.2.3
This is not a real option, but it is included to show how
the present river regime, and all feasible variations to it,
have departed from natural conditions. In the natural
conditions run, Hume and Dartmouth storages are
removed and irrigation demands are set to zero.
Outflows from the Snowy Scheme are replaced with
estimated natural flows.
6.2.2
Benchmark (B42800)
This scenario is a best approximation of the way Hume
and Dartmouth are operated at present. It is a
benchmark, or base case, with which alternative
scenarios are compared.
Features of the scenario are as follows:
• Demand is set at 1993–94 levels.
• Riparian releases are made in accordance with
present rules.
• Hume/Dartmouth harmony releases are made.
Water is transferred from Dartmouth to Hume as
much as possible, while ensuring that Dartmouth
fills in the next season if conditions are wet enough
for Hume to fill. This tends to equalise the
probability of fill of the two storages.
• Releases for hydro-electricity generation at Dartmouth
and Hume are modelled using current rules.
• Pre-releases from Hume and Dartmouth are fully
modelled with combined pre-release targets. The
targets assume minimum inflows and maximum
irrigation demands — based on the logic that the
storage will then always be able to refill if drawn
down to the pre-release target. Pre-release rates are
limited to 10 000 ML/day at Tallandoon and 25 000
ML/day at Doctor’s Point. The recent practice of
sometimes negotiating higher pre-releases from Lake
Hume has not been taken into account in the model.
• Present rates of rise and fall are used.
• Existing flood operating rules (no power station releases
at Dartmouth, use of the top 100 GL of airspace in
Hume to attenuate flood peaks) are modelled.
• Existing practices for Barmah-Millewa forest
watering are modelled. They provide for up to 40
GL of water to be used (i.e. extracted from the river,
not just released from storage for watering or passed
through the forests). An average volume of 21 GL is
actually used: 13 GL evaporated or otherwise lost in
wetlands and 8 GL via small-scale works in NSW.
26
H U M E
A N D
Fill and spill (B42810)
The fill and spill method of storage operation involves
allowing the storage to fill, making no releases for flood
mitigation, and then passing inflows through the
storage by allowing it to spill out of the storage. The
storage then remains full until its level is drawn down
by releases for regulated supply.
The panel modelled this scenario because it was one
of the recommendations from the River Murray
environmental flows scientific panel — particularly
because, at the time of the scientific panel’s findings, no
daily modelling was available to quantify the effects of
the recommendation.
Differences between this run and the benchmark
are as follows:
• No pre-releases are made from either Hume or
Dartmouth.
• No discretional or forced releases for hydroelectricity generation are permitted from Dartmouth
until it is full.
• No Hume/Dartmouth harmony releases are made.
• No attempt is made to use the top 100 GL of the
Hume storage to truncate floods.
Results from the fill and spill scenario show a small
increase in average irrigation diversions, and
corresponding increase in value of irrigation
production. However, in reality, no increase in average
diversions is allowed because they are constrained by
the Cap. Consequently, there are no economic benefits
to the value of irrigation production. Indeed, there are
negative economic impacts on hydro-electricity, salinity,
flood mitigation and tourism. The panel therefore
concludes that overall economic impact from a fill and
spill operation is negative.
The scenario does provide environmental benefits
by improving larger flood events — which also
produces negative economic impacts on human uses of
the floodplain. However, flow variability in small and
medium flow events is non-existent during the pre-fill
period (i.e., during winter months). Consequently, the
fill and spill scenario does not produce a beneficial
environmental outcome.
Over all, the panel considers that the simple fill and
spill scenario has little to recommend it.
D A R T M O U T H
D A M S
O P E R A T I O N S
R E V I E W
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
6.2.4
Provision of airspace (B46770)
This scenario models the idea of providing dedicated
airspace in storages solely for flood mitigation. For
example, if 300 GL of airspace is reserved in a storage
for flood mitigation, that space is only intruded upon to
store floods. As soon as the flood has passed, the water
is released, even if it is not needed for water supply, to
restore the flood cushion.
Various airspace scenarios were modelled:
• space in Hume only,
• space in Dartmouth only,
• space in both,
• maintaining the airspace for the whole year, and
• maintaining it only between June and October.
All runs made with these various scenarios had the
same general effect to varying degrees. Run B46770 is
typical of these scenarios. In this run, the changes from
the benchmark were:
• 200 GL in Dartmouth and 300 GL in Hume are
reserved in June to October solely as airspace to
mitigate floods.
• Triggers for pre-release are reduced by the same
amount.
• If the storage (despite pre-releases) exceeds the
reduced full supply level, releases are maintained at
full channel capacity until the reduced full supply level
(incorporating air space) is achieved. However, this
level is still below total physical capacity of the storage.
• At the end of October, storage operations are
returned to benchmark conditions and, if November
and December inflows are sufficient, the storages
are allowed to fill.
Results of this scenario showed improved economic
benefits to floodplain landholders and modest hydroelectric and salinity benefits. However, these benefits
are far outweighed by penalties to irrigation. Recreation
on Lake Hume also sustained a small economic penalty.
Results indicated an aggregate negative economic effect
of $1.08 million per year.
The panel notes that similar benefits can be
provided to floodplain landholders at a far lower cost to
irrigation by changing pre-release rules (see the
‘Relaxed pre-release rules’ scenario, in the following
section 6.2.5).
Environmental impacts of this scenario are generally
negative. Flows are often released in the wrong season
and at constant rates rather than in a translucent
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
fashion. If the constant flow rates were replaced in
practice by more variable flows, the results may tend
towards a translucent flow scenario.
Translucent flow
The concept of translucency relates to the effect of a dam on
flow. If a dam were to pass all inflow, the flow would be
“transparent”. If a dam were to stop all flow, it would be
“opaque”. In between these hypothetical extremes, the flow is
“translucent” to an extent expressed as a percentage of the
flow released: the higher the figure, the more translucent.
Translucent operation of a storage usually occurs in winter
and spring months. A proportion of daily inflow is released so
that downstream river flows mimic natural variability — but with
reduced magnitude.
For example, 30% translucent operation would indicate that
30% of daily inflow was released to mimic natural conditions.
6.2.5
Relaxed pre-release rules (B42840)
In the benchmark scenario, pre-release rules are
conservative, as they are based on maximum irrigation
demands and minimum inflows. In theory, this should
result in storages always filling in the spring after prereleases are made — so there is never a loss to
irrigation supply. The relaxed pre-release rules scenario
assumes minimum irrigation requirements in the
following season. An assumption of average
requirements was also tested.
In this scenario (relaxed pre-release rules), there are
more pre-releases than under benchmark conditions,
resulting in a benefit to floodplain landholders
marginally greater than in the provision of airspace
scenario. However, economic impacts on irrigation are
less than half those sustained under the provision of
airspace scenario. The relaxed pre-release rules scenario
shows a negative net economic effect of $0.33 million
per year.
Environmental impacts under the relaxed prerelease rules scenario are generally negative in all three
river reaches. There is a minor improvement in
frequency of small floods in the Dartmouth to Hume
reach, but frequency and timing of other events is
generally negative.
Over all, the concept of relaxed pre-release rules has
some merit — but not as a stand-alone scenario.
R E V I E W
27
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
6.2.6
Translucent flows (B46750)
Translucent flows allow a proportion of inflow to a
storage to be passed downstream during the winter and
spring so that downstream flow mimics natural
conditions; however, flow amplitudes are reduced,
depending on the percentage of inflow released. There
would be some adverse effects on regulated supplies,
because releases generally start before there is any
certainty of the storage spilling.
Translucent release policy can be almost infinitely
varied to enhance benefits and minimise costs.
For example:
• varying the percentage released — 10% could be
considered almost opaque, and 100% fully
transparent;
• using different percentages for the two storages;
• varying percentage according to time of year,
volume held in store, time since the last reasonable
flood, etc.; and
• taking only parts of the flow (e.g. allowing the first
500 ML/day to be stored, then passing the next 500
ML/day).
Several variations of translucent flow were examined in
the translucent flows scenario. Based on
recommendations from the River Murray
environmental flows scientific panel, the first scenario
tested was a simple 10% translucent flow in June to
September. Results indicated that 10% was not enough
to produce significant environmental benefits.
A simple 30% translucent flow appeared to produce
unacceptably large effects on consumptive yield
compared to benefits achieved. Various ways of
limiting negative impacts on consumptive yield were
also examined.
Translucent flows scenario run B46750 was a typical
example of a simple translucent scenario. This
scenario varies from benchmark conditions in the
following manner:
• In the months of June to September (subject to
storage levels below), 30% of natural inflows to
both Hume and Dartmouth are passed downstream.
• Benchmark minimum flows below the storages are
maintained — apart from the increased benchmark
flows below Dartmouth when it is more than 60%
full. When Dartmouth is more than 60% full,
benchmark releases are replaced by the
translucency releases.
28
H U M E
A N D
• No translucency releases are made from Hume if
the total capacity of Hume and Dartmouth is less
than 60% of the combined storage capacity.
• No translucency releases are made from Dartmouth
if it is less than 60% full.
• Pre-release and harmony rules are left in place.
Results of this translucent flows scenario indicate that
economic impacts are positive in all areas except
irrigation. However, the impact on irrigation is about
twice the benefits identified for the other areas. The
translucent flows scenario shows a negative net economic
effect of $0.72 million per year.
In general, translucent releases provide significant
environmental benefits because they improve flow
variability and seasonality. Translucent flows scenarios
generating maximum environmental benefit were
found to be those without constraints depending on
volume in store. However, not surprisingly, those
scenarios inflict large penalties on consumptive use.
Suspending translucent flows when storage levels are
low reduces the impact on consumptive use, but
environmental benefits disappear during drought and
when storages are recovering from drought.
A majority of the panel considers that despite the
limitations discussed above, translucent releases appear
to have significant potential to improve environmental
conditions while reducing flood costs in all three
reaches and limiting consumptive-use impacts .
As a stand-alone option, there are some concerns
about the level of impact on consumptive use. Some
panel members believe that the same environmental
benefits may be obtained for less water, by adopting a
more managed approach to flow variation.
6.2.7
Use of Dartmouth power station during
floods (B42801)
Despite the powerful overall flood mitigation effect of
Dartmouth Dam, under certain conditions the duration
of individual floods at some levels is increased (see
section 5.1.2).
Current flood operating rules for Dartmouth prohibit
releases through the power station or irrigation valves
when water is flowing over the spillway if such releases
would cause the flow at Tallandoon to exceed nominal
channel capacity (10 000 ML/day). Generally, this mode
of operation maximises mitigation of flood-peak levels,
but on occasions it extends the duration of floods.
D A R T M O U T H
D A M S
O P E R A T I O N S
R E V I E W
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
It has long been recognised that it is possible to
operate Dartmouth Dam so that it never increases the
duration of a flood (measured as the duration of flow
above 10 000 ML/day at Tallandoon) compared with predam conditions. However, operating that way would, in
some floods, increase the peak flow at Tallandoon above
the flow that occurs under present operating rules.
Scenario B42801 examines the effect of allowing
Dartmouth power station to operate during floods.
Changes in parameters from the benchmark scenario are:
• removal of prohibition on releases through the power
station during spills over the spillway, at times when
flow exceeds 10 000 ML/day at Tallandoon; and
• releases during spills up to the capacity of the power
station (assumed to be 9200 ML/day).
The result is shorter floods — but higher flood peaks —
in the Mitta Mitta valley. The scenario has little effect
outside the Mitta Mitta valley: in fact there are no
significant effects downstream of Lake Hume. In the
Mitta Mitta valley, flood costs to agriculture are slightly
higher ($56 000 per year) but the value of hydroelectric power generation is increased by $476 000 per
year. The scenario generates a net economic benefit of
$420 000 per year.
Marginal environmental benefits are achieved in the
Mitta Mitta reach between Dartmouth and Hume as a
consequence of increasing the frequency of medium and
small flood events. However, no environmental changes
occur in the other two river reaches.
This scenario has net economic benefits and
marginal environmental benefits along the Mitta Mitta
River. The scenario is worth pursuing if increased flood
duration in the Mitta Mitta valley is seen as a significant
problem. However, the panel identifies the following
arguments against implementing this option:
• Dartmouth, on average, increases flood duration at
some levels and decreases them at other levels.
However, it also markedly reduces flood frequency.
Therefore, the argument for decreasing the flood
duration of some floods appears to be a minor issue.
• Aggregate costs to agricultural users of the Mitta Mitta
floodplain appear to be increased a little under this
option.
• Compared with present operation, this scenario would
provide marginal benefits to those with low-lying floodprone land, and marginal (but somewhat larger) penalties
to those with flood-prone but slightly higher land.
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
The panel considers that this is initially a matter for the
Mitta Mitta community to reach an agreed position on, as
it affects no-one else except the operator of the Dartmouth
power station and perhaps the environment to a minor
extent. The power station operator is tied to present
operation under agreements with the Commission or its
agents. However, the operator may be open to negotiation
on this issue: for example, possibly being prepared to
increase contributions to river management funding in
exchange for revised operating rules.
6.2.8
“Sharing the Murray” proposal for the
Barmah-Millewa forest (B47850)
In recent decades, there has been considerable concern
about the effects of River Murray regulation on the
Barmah-Millewa forest area. Consequently, much effort
has been devoted to quantifying those effects and
looking for ways to improve forest watering.
In 1993, the Murray-Darling Basin Ministerial
Council formally resolved to allocate 100 GL of high
security water to the forests — half from Victoria’s
resources and half from New South Wales’. However,
policies and mechanisms to deliver this water have not
been agreed. Under present conditions, an average of
about 21 GL of regulated flow is supplied annually to
the forests. This water is mostly delivered at low flow
rates to stimulate bird and fish breeding. These rules are
incorporated in the benchmark scenario.
In a recent document “Sharing the Murray”, Victoria
has put forward the most recent proposal for a mechanism
to supply this water as part of developing bulk water
allocations for the Victorian side of the River Murray. The
proposal is quite detailed and has been endorsed by the
Victorian Murray Water Entitlement Committee; although,
New South Wales stakeholders have yet to agree with it.
Nevertheless, the panel considers that this proposal is the
best one available for modelling the effects of using this
water for its allocated purpose.
The “Sharing the Murray” proposal was modelled
by replacing benchmark forest watering rules with the
following:
• An account is established to track the high security
water (100 GL per year) and lower security water
(an extra 50 GL in years of reasonable allocation to
irrigators). The account includes rules for limited
carryover and overdraw of water.
R E V I E W
29
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
• During severe drought, the allocation can be
borrowed for consumptive use. However, this loan
must be paid back when irrigation restrictions ease.
This condition reflects natural conditions, as the
forests would have received little water during
severe drought prior to river regulation.
• If there have been no floods for the past four years,
the saved water is released with the target of
producing 500/500/400 GL per month at
Yarrawonga in October, November and December
respectively — or less if not enough water is
available. These are primarily drought-breaking
floods, aimed at filling permanent billabongs,
allowing fish and frogs an opportunity to breed,
providing for limited plant regeneration and
providing a limited opportunity for bird breeding.
• In any year, if spring flows at Yarrawonga exceed
certain trigger levels, the flood is enhanced to 660
GL/month if possible. This provides excellent
opportunities for bird and fish breeding, provides for
plant regeneration including Moira grass, waters the
red gums, and re-establishes the link between the
river and floodplain.
Several variations to the proposal were also modelled:
for example, using a flow trigger at Wangaratta rather
than Yarrawonga, and making variations to trigger
levels. These variations made insignificant differences in
economic and environmental results.
Results indicated that diversions for irrigation
decrease by 26 GL on average. Most of this decrease
occurs in NSW. The scenario increases average forest
consumption of regulated resources from 21 to 47 GL.
The balance of the allocation is spilled before it can
be used, or is released for forest watering and
eventually extracted by water users. To a large extent,
this situation is inevitable because:
• a proportion of the water released from storage for
the purpose of forest watering will flow past the
forests, or through them, and return to the river; and
• storing Barmah-Millewa water from year to year
rather than using it every year means that water
will unavoidably spill from storage in some years.
Economic impacts of this scenario are small benefits to
hydro-electricity generation and salinity, and small costs
to floodplain landholders and Lake Hume recreation.
However, the largest economic effect is the cost to
irrigation. Therefore, net economic effect of the
scenario is calculated to be $1.4 million per year.
30
H U M E
A N D
In environmental terms, this scenario improves:
• long-duration breeding event floods, and
• frequency of shorter floods for forest watering —
although to a more modest extent.
These major benefits occur mainly in the reach of river
below Yarrawonga. However, benefits from increased
medium-sized events in upper reaches could also occur
when large volumes of water are being transferred
down the system to the forests.
The panel considers that while the economic cost is
significant, environmental benefits are also significant.
The panel is also mindful that a decision, in principle,
has already been made by the Ministerial Council to
allocate 100 GL to the forest. An effective means to
deliver the allocation must be developed.
Table 4 Compares natural and benchmark flood regime
in the Barmah-Millewa forest. Flows at Yarrawonga
(1934–1996).
6.2.9
Increased pre-release from Hume Dam
(B46160)
The River Murray Action Group, which represents
floodplain landholders between Hume and Yarrawonga, has
indicated that its members may consider selling easements
over private low-lying flood-prone land. Current nominal
channel capacity is 25 000 ML/day at Albury. The following
scenarios were modelled to assess the effects of three
changes to Hume-Yarrawonga pre-releases:
• Increasing pre-releases to 31 500 ML/day (about
3.5 m at Albury) for pre-releases (run B46160).
• Increasing pre-releases to 31 500 ML/day for all
releases, including those for irrigation supply.
• Increasing pre-releases to 36 000 ML/day
(about 3.8 m at Albury) for pre-releases.
Increasing the nominal channel capacity for pre-releases
was the only change from the benchmark scenario.
The panel considers that increasing nominal channel
capacity to 31 500 ML/day for pre-releases (run
B46160) is the best of the scenarios considered above.
One possible benefit of an increased rate of pre-release
is that watering of the Barmah-Millewa forest should be
improved in years when watering is constrained by
channel capacity between Hume and Yarrawonga.
To investigate effects on forest watering of lifting the
nominal channel capacity, the panel combined the
D A R T M O U T H
D A M S
O P E R A T I O N S
R E V I E W
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
Table 4: Comparison of natural and benchmark flood regime in the Barmah-Millewa forest Flows at Yarrawonga, 1934-1996.
Natural conditions
Current (benchmark) conditions
Jul
Aug
Sep
Oct
Nov
Dec
Year
Jul
Aug
Sep
Oct
Nov
Dec
559
918
837
2036
1501
1043
1934
222
387
202
1329
1582
1005
814
1432
1301
1046
564
282
1935
604
1530
1319
962
441
273
777
2009
1088
686
411
419
1936
318
1659
1191
335
259
337
135
215
751
555
251
153
1937
122
246
336
487
333
476
223
263
383
245
127
21
1938
159
213
198
470
472
469
1164
1997
1646
1487
1174
463
1939
536
1053
1365
1072
842
290
195
257
322
227
150
86
1940
120
243
194
270
485
435
411
303
373
544
255
138
1941
211
190
166
220
294
292
1578
1152
1411
1015
590
330
1942
753
553
583
273
277
297
425
623
815
938
494
205
1943
193
244
289
306
285
334
293
218
178
172
145
77
1944
156
234
204
249
400
476
180
657
679
496
452
174
1945
128
321
236
271
276
287
1603
1511
796
734
559
285
1946
729
802
244
314
333
424
1102
1190
1317
1398
1011
528
1947
473
562
374
469
306
282
338
420
569
703
1117
359
1948
200
217
224
264
383
305
315
435
654
1151
1116
420
1949
147
194
185
470
435
270
381
518
726
977
797
311
1950
152
154
102
145
252
264
1491
1546
1057
1028
597
264
1951
839
1009
750
717
369
269
1852
1196
1905
1292
1467
1062
1952
1903
1199
2035
1210
1492
919
799
1503
1432
1846
1207
468
1953
379
1358
1350
1669
967
296
304
630
621
399
834
711
1954
160
233
211
179
318
577
1091
3185
2139
2306
1287
740
1955
594
3216
2044
2168
1144
326
3305
2435
1958
2092
1290
618
1956
3967
2601
1881
1986
1045
326
556
420
420
610
350
195
1957
225
296
226
295
274
338
927
2758
1218
2257
1023
397
1958
346
1516
776
1876
860
295
163
407
740
719
377
185
1959
115
225
192
270
214
288
1185
1842
1673
1280
715
414
1960
459
988
1371
941
508
304
408
578
607
450
259
177
1961
193
251
177
200
309
372
509
761
629
792
457
234
1962
310
343
213
254
259
284
399
906
870
801
515
246
1963
260
516
326
283
237
318
2188
1437
1570
2358
984
401
1964
923
632
660
1785
667
294
113
522
866
436
308
243
1965
126
339
422
281
289
431
375
876
1248
1291
788
1004
1966
175
386
517
349
265
305
73
142
242
345
144
32
1967
99
212
401
476
472
476
463
1289
937
1548
955
392
1968
308
587
290
363
299
358
1149
889
1203
726
570
394
1969
302
279
803
297
262
269
1020
1930
2224
1380
916
448
1970
407
1259
2100
928
599
282
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
R E V I E W
31
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
(Continued) Table 4: Comparison of natural and benchmark flood regime in the Barmah-Millewa forest Flows at Yarrawonga, 1934-1996.
Natural conditions
Current (benchmark) conditions
Jul
Aug
Sep
Oct
Nov
Dec
Year
Jul
Aug
Sep
Oct
Nov
Dec
487
723
1072
1477
1409
590
1971
264
252
607
805
1007
304
357
541
652
344
186
110
1972
162
238
389
349
293
309
1362
1922
2481
1657
923
403
1973
585
1217
2276
1577
880
314
2509
2523
2345
2986
1517
500
1974
1780
2424
2484
2811
1491
402
1061
1642
2309
2854
1537
692
1975
531
1555
2306
2952
1495
692
162
311
421
1106
461
261
1976
99
231
212
273
242
273
540
601
495
442
215
137
1977
225
150
210
259
295
309
1025
1255
1219
1038
726
542
1978
402
617
382
298
347
276
249
452
1271
1663
565
201
1979
143
202
640
848
264
299
465
792
1006
783
496
366
1980
248
332
290
270
471
476
2813
3347
1653
1198
565
302
1981
1667
2060
1326
745
315
351
170
148
217
165
79
13
1982
113
305
268
338
485
476
819
1478
1970
1305
665
492
1983
405
666
821
271
243
287
230
1493
1696
1567
492
188
1984
126
609
878
928
314
262
271
1305
848
555
395
301
1985
160
670
330
275
278
276
1790
1437
1045
1845
1064
548
1986
883
648
360
698
625
305
879
898
661
513
258
208
1987
463
408
198
274
472
476
1110
795
879
564
422
847
1988
500
313
289
178
266
298
825
1321
1235
1002
835
332
1989
445
686
927
548
438
289
2556
2431
1435
1331
669
243
1990
1600
1657
1397
1077
544
298
666
1326
1870
1072
419
212
1991
251
508
1154
545
265
284
353
931
2183
2808
1389
971
1992
253
509
1450
2360
1255
971
1040
1332
1687
2258
1080
715
1993
986
1306
1656
2291
942
568
354
332
289
359
351
221
1994
168
190
285
465
452
453
2063
1207
986
868
752
577
1995
891
473
563
515
518
284
1041
2192
1498
2778
874
360
1996
537
1862
1302
2404
674
277
increased pre-release from Hume scenario and the “Sharing
the Murray” proposal for the Barmah-Millewa forest
water to be transferred earlier, which may mean
scenario. Results of this combined scenario indicated
that less can be extracted further downstream and
that the economic impact is somewhat greater than for
32
• in other years, the larger channel capacity allows
the “Sharing the Murray” proposal for the Barmah-Millewa
more remains as in-stream flow.
It appears that increased channel capacity does not help
forest scenario on its own. In fact, economic impacts are
Barmah-Millewa watering significantly. A single additional
slightly more than the sum of the two individual
watering event in a century is unlikely to provide much
impacts, probably because:
additional benefit to the forests. However, the larger
• the change in channel capacity only allows the
capacity would allow increased flexibility for varied or
desired volume to be transferred in one extra year,
translucent water releases to Barmah. That additional
1917 (however, the extra volume in that year is
flexibility may provide environmental benefits to both the
quite high); and
Hume-Yarrawonga reach and the reach below Yarrawonga.
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
R E V I E W
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
Table 5: Results of three scenarios exploring increased nominal channel capacity
Nominal channel capacity**
increased to
increased to
increased to
31 500 ML/day for
31 500
36 000 ML/day
pre-releases and
ML/day for
for pre-releases
translucency releases
all releases
and tanslucency
(run B46160)
Average annual flood costs to land
below new channel capacity
Increase in costs to land below new channel
capacity over benchmark
Average annual flood costs to land above
new channel capacity
Decrease in costs to land above new channel
capacity compared to benchmark
$187 000
$198 000
$408 000
$20 000
$31 000
$38 000
$949 000
$949 000
$759 000
$16 000
$16 000
$3 000
To adopt the increased nominal channel capacity for
pre-releases would involve the Commission taking
flood easements over land flooded at flows of about
31 500 ML/day (3.5 m on the Albury gauge). The area
of land directly affected is in the order of 1000 ha.
Some other land would be affected less directly because
it would be inaccessible at times.
The easement could give the Commission the right
to make regulated releases up to 31 500 ML/day:
• during specified months (say June to November) —
but not for the other months of the year, or
• for specified purposes (pre-release and forest
watering) — but not for other purposes.
Considerable consultation and detailed work with those
likely to be affected is needed before the scenario is a
sufficiently robust proposition with reliable cost
estimates. However, an initial estimate is that the cost
of easements — including valuations, negotiation, legal
costs and actual compensation payments — might be in
the order of $3 million to $6 million.
In summary, the benefits of increasing allowable
pre-releases from Hume to 31 500 ML/day are:
• a modest decrease (modelled at $16 000 per year) in
the costs of flooding land above the 31 500GL level;
• substantial environmental benefits to low-level
wetlands — mainly between Hume and
Yarrawonga, but also below Yarrawonga (this is the
main benefit of the scenario);
H U M E
A N D
D A R T M O U T H
D A M S
releases
O P E R A T I O N S
• an enhanced ability to vary pre-releases — whether
by translucency or other more managed means —
which would also improve within-channel flow
variability; and
• a small enhancement in ability to provide a suitable
watering regime for the Barmah-Millewa forest.
Potential costs and risks of the proposal are:
• significant capital cost — possibly in the order of
$3 million to $6 million; and
• even if most of the affected landholders agree with
the proposal, the possibility that a minority may feel
aggrieved.
The panel considers that the increased pre-release from
Hume scenario has potential to:
• improve environmental conditions — primarily
between Hume and Yarrawonga;
• provide a small benefit to flood-prone land above
the 31 500 ML/day flow level; and
• support river management proposals that involve
converting some land from agriculture to riverside
redgum plantation.
Further, the panel recommends that the proposal should
be developed in more detail (subject to acceptance in
principle by those affected) and that it may well form a
useful part of a scenario package.
R E V I E W
33
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
6.3
Scenarios outside the
6.4
scope of the review
Panel members have been acutely aware that other related
work — particularly the Snowy Inquiry and discussion of
environmental flows — had the capacity to affect the issues
being considered in the review. A number of scenarios
were therefore modelled, not because they were options
that would be evaluated in the review, but because it was
necessary to understand the possible effects of them. These
scenarios are as follows:
• Snowy releases increased to 150 GL per year (B46180).
• Combined Barmah-Millewa and Snowy releases
(B47910).
• Irrigation cap reduction of 10% (B46460).
These scenarios helped the panel to place its work in
context with influences outside its terms of reference.
However, the scenarios required so many arbitrary
assumptions that the results were not considered useful
enough to show in this options paper. They are
included in the support paper that provides details of all
the scenarios investigated.
Points of interest were:
• The Snowy releases scenario had about the same
effect on consumptive use as the “Sharing the Murray”
proposal for Barmah-Millewa forest scenario. However,
no real conclusion can be drawn from the Snowy
releases scenario, because of the uncertainty of
measures that might be put in place to offset
increased Snowy diversions. The report of the Snowy
Inquiry quantifies Snowy proposals in detail.
• The combined Barmah-Millewa and Snowy releases
scenario showed the expected negative economic
impacts. However, most of the benefits of the forest
watering scenario remained, even with the
reduction of total water in the Murray.
• The irrigation cap reduction of 10 percent showed
that, although the volume used for irrigation was
reduced by 10 percent in each state, the value of
irrigated production was reduced by a smaller
amount — about 8 percent in NSW and only 2
percent in Victoria. This is because the irrigation
enterprises affected will be the lower value ones;
water would flow by trading to the higher value
enterprises so their production would be unaffected.
This seems reasonable in qualitative terms, but it
may be stretching the model beyond its capability to
place much reliance on the quantitative result.
34
H U M E
A N D
Combined scenarios
Five similar combined scenarios, but with significant
differences, were modelled. All included the following:
• The “Sharing the Murray” proposal for the BarmahMillewa forest.
• Harmony operation of Hume and Dartmouth as
specified in the benchmark run.
• Channel capacity between Hume and Yarrawonga
increased to 31 500 ML/day for the purpose of
translucency releases or pre-releases but not for
regulated releases. Effectively that would mean the
increased capacity would apply in most years
between June and October or perhaps November.
The differences were as shown in table 6.
The results are set out in table 7, and conclusions
can be drawn as follows:
• In terms of economic impact, they can be divided
into two groups. Scenarios A, B and E each
constrain the volume of non-consumptive release
either via pre-release rules or by cutting off
translucent releases when storage levels drop. Each
has a negative net economic impact in the order of
$3 million per year. Scenarios C and D include
translucent releases unconstrained by low storage
levels, and each has a negative net economic impact
in the order of $10 million per year. The economic
impacts are dominated by irrigation.
• In all scenarios, there are economic benefits to
floodplain dwellers below Hume, and decreased
salinity costs. Decreased salinity costs derive from
higher instream flows, and may also be of some
minor environmental advantage.
• The indicators of environmental effects shown in
the table are a selection of those produced during
the review. The panel has found it difficult to come
up with a clear assessment of environmental
advantages and disadvantages, because each
scenario involves some sort of environmental tradeoff — an improvement in one area, but a decline in
another. For example: translucency, in general,
increases flood frequency in spring, but can reduce
the number of long-duration breeding event floods.
• Nevertheless, in terms of environmental impact,
scenarios C and D are clearly superior to the other
three below Yarrawonga and, perhaps less
demonstrably, between Hume and Yarrawonga. On the
Mitta Mitta River, fewer environmental effects are
D A R T M O U T H
D A M S
O P E R A T I O N S
R E V I E W
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
Table 6: Differences between the five combined scenarios
Package
30% translucency releases
A
B
C
D
E
yes
yes
yes
yes
no
60%
60%
0%
0%
not applicable
as in
none
as in
none
based on
made in June to September
Storage capacities below which
translucency is turned off
Pre release rules
benchmark
benchmark
run
run
minimum
irrigation
demands
apparent, though all of the proposals with translucency
are expected to deliver environmental benefits.
• Scenario E is shown as the worst from the
environmental point of view, probably because of
the lack of translucent releases as modelled.
It is important to understand that the amount of
resource committed to instream flows can be decided
independently of the mechanism used to provide those
instream flows in a suitably varied manner. For
example, it would be possible to decide the degree of
risk of storages failing to fill that should be taken when
pre-releasing. The effect on consumptive use could be
determined by modelling. When that issue was
resolved, by whatever process, pre-release rules could
be developed to set end-of-month target storages in
accordance with the agreed level of risk. It would then
be possible to operate from day to day on a translucent
(or more planned) varied release basis rather than a
fixed release basis.
In considering what amounts to a possible transfer of
water from consumptive use to instream use, irrigators
make the point that their existing water use is covered
by some form of property right. The precise nature of
this right varies between states, between different
locations within states, and between different water
uses. Transfer is likely to be a continuing process as
instream flow requirements are better identified. It is
therefore important to set up an on-going process to
explicitly change the property rights held by irrigators.
In summary, there is a very clear trade-off between
economic impact and environmental benefit. This can
be illustrated, in broad terms, by table 8. It compares
scenario A (which is typical of the A, B and E group)
with scenario C (which is similar to D). The only
difference between A and C is that in scenario A the
30% translucent releases are turned off if storage
volumes fall below 60%. In scenario C it remains,
irrespective of storage volume.
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
R E V I E W
35
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
Table 7: Results of the five combined scenarios
Run Number
Run description
B42800
Natural
Conditions
Benchmark
DOLLAR IMPACTS
Absolute
Absolute
B48190
B48200
B48210
B48220
B48230
Package Package Package Package Package
A
B
C
D
E
DOLLAR IMPACTS
Difference (this run minus Benchmark)
FLOODING (1934-1997
Mitta Mitta at Tallandoon
Floods/year
Average days flooded/year
Average flood costs/year ($000)
1.21
19
506
0.37
12
244
0.05
0
-24
0.03
1
2
0.10
0
-14
0.11
2
14
-0.05
-2
-53
1.38
48
2394
0.70
26
1133
-0.05
-2
-142
-0.01
-1
-102
-0.03
-4
-220
-0.03
-3
-183
-0.14
-5
-229
1.02
23
1358
0.54
13
654
0.00
-1
-88
0.00
-1
-63
-0.02
-1
-93
0.00
-1
-69
-0.08
-2
-115
0
0
0
1 888
2 518
222 478
-36
-259
-3 341
-35
-261
-3 224
-101
-131
-9 415
-100
-131
-9 317
-29
-81
-2 603
0
0
0
1 624
841
329 327
-10
0
-276
-10
0
-270
-25
43
-1 121
-24
43
-1 112
-10
0
-305
0
396
15
16
40
44
21
0
0
97
263
4 254
-15
10
166
-1
4
93
-15
-1
23
-3
-6
-44
-20
13
181
0
3 989
-75
-96
-159
-172
-64
0
0
-4 258
0
551 804
8 243
-66 633
-2 031
2 184
-3 617
91
202
254
-90
-3 494
-4
336
164
-89
-10 537
-136
486
328
-193
-10 428
-216
579
238
-192
-2 908
117
187
398
-77
-
493 568
-3 160
-3 087
-10 052
-10 020
-2 282
Murray at Albury
Floods/year
Average days flooded/year
Average flood costs/year ($000)
Murray at Tocumwal
Floods/year
Average days flooded/year
Average flood costs/year ($000)
IRRIGATION (1891-1997)
New South Wales
Average diversions (GL)
Maximum shortfall (GL)
Average production value ($000/year)
Victoria
Average diversions (GL)
Maximum shortfall (GL)
Average production value ($000/year)
South Australia
Maximum shortfall (GL)
HYDRO ELECTRIC GENERATION
Dartmouth (1934-1997)
Average volume spilled (GL/year)
Average power generated (Gwh/year)
Value of power generated ($000/year)
Hume (1891-1997)
Value of power generated($000/year)
SUMMARY OF DOLLAR IMPACTS ($000/yr)
Irrigation (1891-1997) NSW+Vic
Hydro electricity
Salinity
Flooding (1934-1997)
Hume recreation (1891-1997)
Total dollar benefit ($000/year)
NON DOLLAR IMPACTS
Absolute
Absolute
NON DOLLAR IMPACTS
Difference (this run minus Benchmark)
DARTMOUTH TO HUME REACH
Floodplain inundation (1+ day floods Jun-Dec)
No. years with an event > 13 000 ML/day
No. years with an event > 19 000 ML/day
43
36
18
9
2
1
1
1
3
3
3
3
0
-1
1 153
1 244
0
-6
-2
-8
10
57
52
42
27
1
-1
1
-1
0
1
1
1
1
-1
4 016
5 070
54
28
76
52
114
61
53
57
36
3
-1
3
-1
4
2
4
2
4
-1
3 378
3 475
70
63
91
84
71
45
24
9
20
28
-16
29
-16
24
-14
25
-14
22
-12
98
73
68
55
37
29
5
-3
3
5
-3
1
9
0
4
8
0
3
2
-1
3
93
72
45
33
1
1
1
1
2
3
2
3
0
1
Channel stability
Average annual flow within river banks (GL)
HUME TO YARRAWONGA REACH
Floodplain inundation (1+ day floods Jun-Dec)
No. years with an event > 25 000 ML/day
No. years with an event > 31 500 ML/day
Channel stability
Average annual flow within river banks (GL)
BELOW YARRAWONGA
Floodplain inundation (7+ day floods Aug-Jan)
No. years with an event > 14 000 ML/day
No. years with an event > 25 000 ML/day
Channel stability
Average annual flow within river banks (GL)
Bird & fish breeding indicators (over 106 yrs)
No of "excellent" years
No of "good" years
Barmah Forest watering indicators (106 yrs)
Years with 1 month or more > 550 GL (Yarra)
Years with 1 month or more > 912 GL (Yarra)
Years with 1 month or more > 1039 GL (Yarra)
Hattah Lakes watering indicators (106 yrs)
Yrs 1 month or more > 1116 GL (flow to lakes)
Yrs 1 month or more > 1487 GL (good floods)
36
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
R E V I E W
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
Table 8: Trade-off between economic impact and environmental benefit
Combined
Combined
Scenario A
Scenario C
(translucency only
(translucency
if storages more
at all storage
than 60% full)
levels)
SUMMARY OF DOLLAR IMPACTS ($000/year)
Irrigation — New South Wales
-3341
(-1.5%)
-9415
(-4.2%)
— Victoria
-276
(-0.1%)
-1121
(-0.3%)
Hydro-electricity
+ 91
(+1.1%)
-136
(-1.6%)
Salinity
+202
(+0.3%)
+486
(+0.7%)
Flooding
+254
(+12.5%)
+328
(+16.1%)
-90
(-4.1%)
-193
(-8.8%)
-3160
(-0.6%)
-10052
(- 2.0%)
Hume recreation
Total dollar benefit ($000/year)
SUMMARY OF NON-DOLLAR IMPACTS
Dartmouth – Hume reach
little change
little change
Hume – Yarrawonga reach
slightly better
slightly better
Below Yarrawonga
Bird breeding (excellent + good years)
% shift towards natural
Forest watering (sum of low + high level)
% shift towards natural
Hattah Lakes watering (sum of low + high level)
% shift towards natural
The phrase “% shift towards natural” is an indication of
how far the scenario moves that indicator from the
benchmark value towards the natural conditions value.
For example, the sum of excellent and good years for
bird breeding is 69 years under natural conditions and
29 years under benchmark conditions — a difference of
40 years. Combined scenario A produces 12 more of
these years than the benchmark scenario, which is a
shift of 30% from benchmark to natural.
The table highlights fundamental questions faced by
the panel to which, as yet, it has no firm answers. The
questions are:
• Are the benefits under A or B sufficient for
sustainability?
• Is it worth $3 million a year, or 0.6% of the
productive value of the water supply system, to
produce the benefits shown under combined
scenario A — and if so, who should pay?
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
+12
+10
+30%
+25%
+8
+13
+10%
+16%
+2
+5
+2%
+6%
• Is it worth $10 million a year, or 2% of the
productive value of the water supply system, to
produce the benefits shown under combined
scenario C — and if so, who should pay?
• Is the second set of benefits three times as valuable
as the first set?
• How do we deal with the reality that irrigators hold
property rights to the water they consume? These
rights exist in all three states, though they are
stronger in Victoria and SA than in NSW.
Despite its inability to answer these questions
definitively, the panel considers that combined
scenarios of the sort described above hold considerable
promise for producing worthwhile environmental
improvements at tolerable economic cost. It seeks
opinions from the wider community on where the
balance between competing interests should lie.
R E V I E W
37
7. Summary of options and preliminary panel views
These conclusions simply collect and
repeat the options identified and the
example, possibly being prepared to increase
contributions to river management funding in
exchange for revised operating rules.
preliminary views of the panel. They
Adverse effects on agricultural land at peak regulated flow
are re-arranged in river reaches as far
The panel considers that there are three options for
resolving this problem:
• investigate nominal channel capacities in the range
9000 to 10 000 ML/day,
• investigate construction of regulators where
appropriate, or
• take flood easements over affected land and pay
appropriate compensation.
The panel has further considered these options in light
of the following factors:
• problems may be minimised by carefully selecting
the regulated release figure,
• regulators would probably only be required on one
or two properties, and
• easements could be taken over the affected land if
no structural solution is possible.
The panel considers that further investigations should
be conducted to ascertain the most beneficial option for
each affected property.
as possible.
7.1
Dartmouth – Hume reach of river
Effect of Dartmouth Dam on pasture productivity
The panel notes that possible increased water
allocations and pricing concessions are currently being
assessed by Goulburn-Murray Water: they cannot now
be influenced directly by the Operations Review.
The following additional options were identified:
• Investigate earlier pre-releases in years when
Dartmouth Dam has spilled, to avoid periods of low
flow between spring spills and autumn harmony
releases.
• Investigate lower and earlier releases in years when
resources must be transferred from Dartmouth to
Hume for supply.
The panel’s preliminary views are that:
• Current harmony rules provide for releases as soon
as practicable following Hume ceasing to spill.
• When Dartmouth releases are needed for supply
purposes, there may be some scope for earlier
releases at lower rates; however, this could involve
increased resource loss risk.
Flood duration in the Mitta Mitta valley
Despite the powerful flood mitigation effect of Dartmouth
Dam, under certain conditions the duration of individual
floods at some levels is increased. By using the power
station during floods, it is possible to eliminate this effect.
Peak flood levels would then sometimes be higher, but
still less than under natural conditions.
The panel considers that initially this is a matter for
the Mitta Mitta community to reach an agreed position
on, as it affects no-one else except the Dartmouth
power station owner and perhaps the environment to a
minor extent. The power station owner is tied to
present operation under agreements with the
Commission or its agents. However, the power station
operator may be open to negotiation on this issue: for
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
Erosion on the Mitta Mitta River
Based on the submissions received and analysis
conducted by the panel, the following options have
been identified:
• Continue with existing stream erosion control
methods, accepting that the result over time will be
a willow and rock lined river channel of limited
environmental value.
• Fund further research into mechanisms and factors
contributing to bank slumping on the Mitta Mitta River.
• Develop an integrated program of waterway and
floodplain management along the lines suggested by
the NECMA.
The panel’s preliminary view is that an integrated
program of waterway and floodplain management along
the lines suggested by the NECMA should be developed.
Impact of Dartmouth Dam on water
temperature and quality
Based on the submissions received and analysis
conducted by the panel, the following options have
been identified:
R E V I E W
39
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
• No action — accept that temperatures in the Mitta
Mitta River will remain depressed, and that the river
ecology will remain altered from its natural state.
• Install shutters on the existing high-level outlet to
provide limited improvement.
• Raise the top of the existing structure to above full
supply level and install a fully functional multi-level
offtake.
• Agree in principle that a fully functional offtake is
required, and conduct detailed investigations into
the cost, benefit and optimum way to achieve a
fully functional offtake.
The panel’s preliminary view is that it agrees in
principle that a fully functional offtake is required and
that detailed investigations into the cost, benefit and
optimum way to achieve a fully functional offtake must
be undertaken.
7.2
Hume to Yarrawonga reach of river
Adverse effects on agricultural land
peak regulated flow
The panel considers that options for dealing with this
problem are to:
• reduce peak regulated flow level to a figure
significantly lower than 25 000 ML/day;
• do nothing, on the basis that the negative impacts
are outweighed by flood mitigation benefits to
agricultural land; or
• take flood easements over the affected land and pay
appropriate compensation.
The panel considers that, for equity reasons, taking
flood easements over the affected land and paying
appropriate compensation is the only reasonable option.
The need for a comprehensive river management plan
between Hume and Yarrawonga
addressed by developing a comprehensive, properly
funded program for management of the reach. The
management program will initially need a strategic
approach to articulate a vision for the future
desirable state of the river. The strategic framework
will require:
• developing criteria for acceptable and unacceptable
erosion rates (and acceptable methods of erosion
control);
• setting limits to acceptable rates of channel
widening and bed degradation;
• a decision on the extent to which anabranch
development needs to be contained;
• setting desired levels of protection for aquatic and
riparian habitats; and
• documenting desired aesthetic and recreational values.
Based on the strategic framework, a comprehensive
river management program should be developed. This
program would:
• establish an agreed management arrangement
(which needs to work in two states, have proper
local input, etc);
• establish links with associated land management
programs in each state;
• establish agreed funding arrangements — with
consideration of funding from such sources as the
Murray-Darling Basin Commission, catchment
management authorities, local government and
input (cash or kind) from landholders;
• set a works program — including both an annual
program of necessary patch-up works (done now to
a modest extent with MDBC funding) and a
coordinated strategy of activities designed to achieve
the long-term goals; and
• monitor progress and the extent to which the
strategic framework might need to be changed.
Increased pre-release from Hume Dam
The panel considers that future options for
management of this reach of the Murray are to:
• retain the present management arrangement —
under which the Commission provides limited
funding to the NSW Department of Land and Water
Conservation to treat actively eroding sites on a
priority basis; or
• develop a comprehensive, properly funded program
for management of the reach.
The panel believes that this issue can only be fully
40
H U M E
A N D
In summary, the benefits of increasing allowable prereleases from Hume to 31 500 ML/day are:
• a modest decrease (modelled at $16 000 per year)
in the costs of flooding land above the 31 500GL
level;
• substantial environmental benefits to low-level
wetlands — mainly between Hume and
Yarrawonga, but also below Yarrawonga (this is the
main benefit of the scenario);
D A R T M O U T H
D A M S
O P E R A T I O N S
R E V I E W
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
• an enhanced ability to vary pre-releases — whether
by translucency or other more managed means —
which would also improve within-channel
variability; and
• a small enhancement in ability to provide a suitable
watering regime for the Barmah and Millewa
forests.
Potential costs and risks of the proposal are:
• significant capital cost — possibly in the order of $3
million to $6 million; and
• even if most of the affected landholders agree with
the proposal, the possibility that a minority may feel
aggrieved.
The panel considers that the increased pre-release from
Hume scenario has potential to:
• improve environmental conditions — primarily
between Hume and Yarrawonga;
• provide a small benefit to flood-prone land above
the 31 500 ML/day flow level; and
• support river management proposals that involve
converting some land from agriculture to riverside
redgum plantation.
Further, the panel recommends that the proposal
should be developed in more detail (subject to
acceptance in principle by those affected) and that it
may well form a useful part of a scenario package.
7.3
Conclusions that are not reach-specific
Effects of regulated flow and rain rejections on natural
drying cycles in wetlands
The panel considers that this issue will require
considerably more work, integrated into river flow
management plans, and that solutions are likely to
involve the following:
• Improved river operation. Improved river operation
may be possible from better weather forecasts, more
accurate ordering from irrigation agencies, and
improved estimation of river losses.
• Retention of rain rejections in storage of some kind.
Four possibilities have been identified, as follows:
– storage on-farm;
– storage in distribution channels;
– continued emphasis on drainage diversion
permits; and
– provision of storage airspace in some weir pools.
H U M E
A N D
D A R T M O U T H
D A M S
O P E R A T I O N S
• Physical works on individual wetlands. Works
would consist of banks, regulating structures and
perhaps pumps to control the extent to which water
was introduced into, or kept out of, a particular
wetland at different times of the year.
Again the panel considers that it is likely that the
Interstate Working Group on River Murray Flows will
need to consider this issue in some detail.
The need to better manage minimum flows
downstream of Mildura
The panel considers that there are three options for
resolving this problem, as follows:
• Obtain more precise orders from diverters. Orders
for major diversion points (Red Cliffs, etc.) are
received a week in advance, but are not always
adhered to. Private diverters are relatively
uncontrolled.
• Utilise more storage volume in weir pools. Most weir
pools are operated at almost constant levels, which
is convenient for water diverters and boating
interests but provides little or no scope to reregulate water. The constant pool levels also have
environmental disadvantages.
• Improve measurement. However, this action is really
incidental to improved flow control.
The panel considers that all the options above can be
adopted. This issue is essentially one of better flow control
in this reach of river — operation of Hume and Dartmouth
Dams has no direct effect on control of these flows.
The need for improved communication
The panel has concluded that formal, continuous
liaison should be set up between the Murray-Darling
Basin Commission (or River Murray Water) and
interested community groups. This liaison should be:
• regarded as a permanent commitment — not just
something to be fitted in when time is available; and
• of a frequency and form negotiated with particular
interest groups to suit their needs.
7.4
Broad conclusions from modelling
• A simple fill and spill arrangement appears to have
few benefits in economic or environmental terms.
• Airspace scenarios do not present adequate benefits
in return for costs. The same advantages to
floodplain landholders can be obtained at far less
R E V I E W
41
H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
cost to irrigators by changing pre-release rules. By
changing pre-release rules from the present
conservative rules (that take almost no risk of failing
to fill) to rules that allow a specified risk, more
airspace is created but often the storages do fill and
consumptive use is not affected. In contrast, simple
airspace rules impose near certainty of failing to fill
and, in effect, reduce the volume of storage useful for
water conservation by the airspace volume.
• Translucent flow scenarios show considerable
promise. The simple 10% translucency rule is not
enough to produce worthwhile environmental
benefits but 30% translucent flows produce
worthwhile benefits. However, adverse effects on
consumptive yield need to be minimised in some
way. Conceptually, adverse effects could be
minimised by setting storage targets in the same
manner as with current pre-release rules (possibly
building in a defined risk of failing to spill), and
then operating from day to day on a translucent
rather than fixed release basis.
• Allowing pre-releases and Barmah watering releases
to be made up to an increased nominal channel
capacity (e.g. 31 500 ML/day between Hume and
Yarrawonga) has little benefit to forest watering, but
the increased channel capacity would allow more
freedom for translucent-type releases.
• Using Dartmouth power station during floods
would have significant net economic benefits and
marginal environmental benefits. This scenario
42
H U M E
A N D
could also ensure that flood duration is not
increased. There would be a small cost to
agriculture in the Mitta Mitta valley, but there
would be no effects below Hume.
• The scenario that models the “Sharing the Murray”
proposal to water the Barmah-Millewa forest
provides good increases in low-level flooding but
has less effect at higher levels. Variations to the
proposal produce very little difference in either
benefits or penalties.
Modelling of combined scenarios
The panel considers that a package of operational
policies can be developed on the basis of the modelling
results. This package could include:
• a mechanism for watering the Barmah-Millewa
forest,
• some form of varied releases (for example,
translucent releases), and
• possibly an increase in nominal channel capacity
between Hume and Yarrawonga for pre-releases
and forest watering releases.
The key issue is the balancing of environmental benefit
against economic cost.
The panel has formed the view that combined
scenarios of the sort described above hold considerable
promise for producing worthwhile environmental
improvements at tolerable economic cost. It seeks input
from the wider community on where the balance
between competing interests should lie.
D A R T M O U T H
D A M S
O P E R A T I O N S
R E V I E W
Appendix A: Terms of reference for the
Operations Review
Purpose
To review the current operating procedures for Hume
and Dartmouth Dams and recommend how they may
be amended to address the competing objectives of
water supply, environmental enhancement and flood
mitigation. The review will take into account:
• impacts of current and alternate operating
arrangements for the Dams on farming and other
groups who occupy the floodplain and on other
components of the Murray-Darling systems;
• the current arrangements for determining target
storage levels aimed at balancing flood mitigation,
water supply and environmental objectives and a
range of alternative strategies and their impacts;
• the current River channel capacity rules
downstream of the Dams and whether these can be
modified to improve outcomes; and
• the provisions of the Murray-Darling Basin Agreement.
In considering these issues, the review should take into
account the Ministerial cap on water diversions, cost
sharing, economic, social and environmental factors.
The review should consider what, if any, other actions
(i.e., land-use planning measures) are warranted and
comment on any implications for the operation of other
major storages.
Modus operandi
The Study will be conducted by a Project Manager
appointed by the Commission. The Project Manager’s
role is to:
• ensure the Terms of Reference are addressed
• manage all the necessary input to the study
• contract all the necessary technical skills for the Study
• manage the budget for the Study
• convene and support a reference panel
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• convene as necessary meetings of targeted
stakeholder groups
• ensure the information generated is provided to the
Commission.
Reference panel
The reference panel will consist of representatives as
follows:
• 1 Commission;
• 1 Community Advisory Committee;
• 1 Local Government;
• 1 Mitta Mitta valley;
• 2 Hume to Yarrawonga Reach (1 from each State);
• 3 irrigators (1 Vic gravity, 1 NSW gravity and 1
pumped districts);
• 2 environment (1 Vic and 1 NSW); and
• 3 operating authority reps (1 Vic, 1 NSW, 1 SA).
The Commission representative would chair the
Reference Panel. Arrangements for the conduct of the
Reference Panel will be provided.
Time frame
The Study will commence on 1 January 1997 and be
completed by 30 September 1997. The Project Manager
will report on a regular basis to the Commission.
Progress reports are to be provided to the March and
June Commission meetings with a draft of the final
report being available by 1 September 1997. A draft
report will be released for public comment for a period
of six weeks. The final report is to be in a form suitable
for public release.
[Note: Early in the review, it was recognised that the
original timing was unachievable if a thorough review
was to be carried out. Hence, the Commission agreed to
extend it].
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Appendix B: Reference panel members
Chair
Brian Haisman
(02) 6279 1061
Members
Allan Curtis, replaced by Noelene Wallace
Community Advisory Committee
(02) 6027 5322
Stuart Anderson
Local government
(03) 5480 9558
Tom Martin
Mitta Mitta valley
(02) 6072 0384
Arch McLeish
Tourism / recreation / Albury-Wodonga
(02) 6043 2244
Ian Lobban
Hume — Yarrawonga reach
(02) 6026 7255
Richard Sargood
Hume — Yarrawonga reach
(02) 6035 0555
Lance Gardiner
NSW gravity irrigators
(03) 5882 3583
Alan Major
Vic gravity irrigators
(03) 5456 8314
Pat Lanigan
Sunraysia district
(03) 5025 7285
Dietrich Willing
Environmental interests
(02) 9396 8408
Tim Fisher
Environmental interests
(03) 9416 1166
David Harriss, replaced by Mel Jackson
NSW operating authority
(02) 6041 1650
Garry Smith
Vic operating authority
(03) 5833 5480
Andrew Jessup/ Phil Pfeiffer
SA operating authority
(08) 8204 1513
Monica Morgan
Aboriginal interests
(03) 5869 3353
Kevin Ritchie
Dept Nat Resources & Environment Vic
(03) 5761 1611
Jody Swirepik
Environment Protection Authority NSW
(02) 6299 3330
Anne Jensen
replaced by Paul Harvey
Dept Environment, Heritage
and Aboriginal Affairs SA
(08) 8204 9137
Clarke Ballard
Project Manager
(02) 6279 0176
Michelle Cowan
MDBC
(02) 6026 4320
Neville Garland
MDBC
(02) 6279 0136
Non-voting members
Project team
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Appendix C: Key issues identified in scoping study
• Need for better information from Commission and
better communication with interest groups.
• Consumptive yield and security of system.
• Use of dams to mitigate floods:
– benefits and adverse effects on downstream
agricultural land,
– adverse environmental effects.
• Time of year of releases.
• Releases for generation of hydro-electricity.
• Impacts on the recreation industry:
– flooding of caravan parks,
– effects of low levels in Lake Hume,
– importance of accurate flood prediction.
• Temperature impacts of releases from different
storage levels.
• Water quality, particularly salinity and algal blooms.
• Impacts of river regulation on flora and fauna.
• Impacts on river ecology.
• Impacts on salinity and other water quality
parameters.
• Impacts on riparian landholders of peak regulated
flows.
• Effects of rising and falling river levels, and
regulated releases generally, on bank erosion.
• The changing shape of the river channel, and its
impact on flooding over time.
• Interstate water sharing arrangements:
– Murray Darling Basin Agreement,
– Snowy Mountains Agreement,
– effects of privatisation of Snowy Scheme.
• Effects of the Ministerial cap on diversions.
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Appendix D: Details of “Backgrounder” papers
No 1
Review of the operation of Hume and
No 5
Dartmouth Dams
•
•
•
•
•
•
Terms of reference
Key questions
Demands on the system
Extent of change
Conduct of the review
Reference panel
No 2
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
No 6
Lake Hume — Overview of Operation
Summary
Filling phase
Release phase
Pre-release phase
Spilling (flood) phase
Power station
Rates of rise and fall in River Murray
Special circumstances
No 4
Dealing with the Capacity Constraints
of the Barmah Choke (in preparation)
The regulated Murray
Natural flow pattern
River Murray Waters Agreement
Distribution of water
Major storages
The Snowy Mountains scheme
Barrages, weirs and lock
No 3
Introduction
Releases for water supply
Data exchange
Entitlement releases
Above-target releases
Flood releases
Rates of rise and fall
Regulation and Distribution of River
Murray Waters
•
•
•
•
•
•
•
Dartmouth Power Station — Overview
of Water aspects of Operation
•
•
•
•
•
•
•
•
Origin of the Barmah-Millewa forest
Peak water demands
when the Choke causes problems
Ways around the Barmah Choke capacity problem
Impact on water trading
Past work on capacity of the Choke
Other capacity constraints on the Murray
The future
No 7
•
•
•
•
•
•
River Murray Flow Management
The broader context
Background to instream flows
Outcomes
Community participation
Progress to date
Further reading
Lake Dartmouth — Overview of
Operation
•
•
•
•
•
•
•
•
•
Summary
Filling phase
Release phase
“Harmony” transfer to Hume
Pre-release phase
Spilling (flood) phase
Power station
Rates of rise and fall in the Mitta Mitta River
Special circumstances
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Appendix E: Issue register
Dartmouth to
Hume
Relevant to reach:
Hume to YarraEchuca
Yarrawonga to to
wonga
Echuca
Mildura
Downstream of
Mildura
Relevance
to Hume–
Dartmouth
Review
Priority as
issue for
Review to
address by
modelling
Priority
as issue for
Review to
address (not
bymodelling)
Limitations to water supply
by cap
•
•
•
•
•
Med
Low–med
—
Potential lowering of security of supply
system, including entitlement flows to
South Australia
•
•
•
•
•
High
High
—
External influences: e.g. possible
adverse effects of changes in Snowy
Scheme environmental flows or
management, changed operation of
Lake Victoria
•
•
•
•
•
Med
—
Low
•
•
Low
—
Med
ISSUE
WATER SUPPLY
Inadequate minimum flows
downstream of Mildura
Transmission and operational
losses in river
•
•
•
•
Med
—
Med
Transmission and operational losses
in distribution systems (ie off river)
•
•
•
•
Low
—
Low
River levels — advice and forewarning
of changes inadequate
•
•
•
•
Med
—
Low
Adequacy of licence volumes on
Mitta Mitta and below Hume; need for
irrigation to maintain production
•
•
Low
—
—
Limitations to water supply imposed
by limited river channel capacities
•
•
•
•
High
Low
—
•
•
•
Med
—
Low (high on
Mitta Mitta)
Med
—
Low–med
High
High
High
High
High
High
High
High
High
High
High
—
High
Med
Med
High
High
High
High
High
High
High
—
High
High
High
High
Inadequate minimum river levels —
foot valves out of water
(communication issue?)
•
•
Effects of water temperature on
agricultural production
•
•
Is management of airspace as good
as it should be?
•
•
•
Flood mitigation may have adverse
environmental effects — what is the
best environmental solution?
•
•
•
Are “harmony” rules optimal?
•
•
Effect of Dartmouth in lengthening
some floods — operate power station
or valves during floods? Different
operation of re-regulating pondage?
•
FLOOD MITIGATION
Effect of Hume/Dartmouth on floodplain
productivity, water tables etc
•
•
Possible pre-release strategies for
regaining airspace — agricultural and
environmental effects
•
•
•
Pre-release methods — what other
techniques could be used?
Variable flows sometimes above
channel capacity?
•
•
•
Adverse effects on small area of land
at peak regulated flow levels
•
Effect of various operating strategies
onland which is flood-prone but above
regulated flow levels
•
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•
D A M S
•
•
•
•
•
O P E R A T I O N S
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H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
ISSUE
Dartmouth to
Hume
Relevant to reach:
Hume to YarraEchuca
Yarrawonga to to
wonga
Echuca
Mildura
Downstream of
Mildura
Relevance
to Hume–
Dartmouth
Review
Priority as
issue for
Review to
address by
modelling
Priority
as issue for
Review to
address (not
bymodelling)
•
•
•
•
High
Med
Med
•
•
High
High
High
ENVIRONMENT
Minimum flows — are they adequate
and seasonally acceptable?
Adequacy of flood events for watering
of the Barmah–Millewa area
•
Adequacy of flood events for wetland
and forest watering in general
•
•
•
•
•
High
High
High
Environmental releases — release % of
inflow, release on top of flood peaks etc?
•
•
•
•
•
High
High
High
•
•
•
•
Med
Low
Low
•
•
Med
—
High
Management of weir pools —
as lakes or variable regimes?
Need for river management plans —
includes willow encroachment,
management of riparian zone
•
Natural flooding in the lower reaches
of the river
Effect on environment of rapid drops
in river level (especially lower river)
•
•
Environmental effects of temperature
ofwater released
•
•
Effect of regulated flows and rainfall
rejections on ability to restore natural
drying cycles in wetlands
•
•
•
•
•
•
•
•
Med
Med
Med
•
•
Med
—
Med
Med
—
Med
High
—
High
Med
—
Med (high for
Dartmouth)
•
•
WATER QUALITY
Possible improvements to quality of
releases — anoxic water, iron,
manganese, temperature
Effects of possible flow regimes on
salinity levels
Algal management — provision of
sufficient flow to dispel blooms
•
•
•
•
Med
Low–med
Low–med
•
•
Low
—
Low
•
Low
—
Low
•
Low
—
— (manage
at source)
High
High
High
Med
—
Low
Low
—
—
High
—
High
Lower Murray water quality — need
for Murray flows rather than Darling at
least one year in three
Management of phosphorus levels
•
•
•
•
•
•
•
CHANNEL STABILITY
Effects of possible Hume/Dartmouth
operating regimes on channel stability
and channel capacity
Effect of weir operation and river
regulation on rate of fall in river level
(especially lower river)
Effects of willow encroachment and
riparian zone management on channel
stability and channel capacity
Understanding of main channel and
anabranch issues between Hume
and Yarrawonga
52
•
•
•
•
•
•
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Dartmouth to
Hume
Relevant to reach:
Hume to YarraEchuca
Yarrawonga to to
wonga
Echuca
Mildura
Downstream of
Mildura
Relevance
to Hume–
Dartmouth
Review
Priority as
issue for
Review to
address by
modelling
Priority
as issue for
Review to
address (not
bymodelling)
Who pays? (includes possible effects of
Snowy increment on channel stability)
•
•
•
•
•
High
Med
High
Effects on channel erosion of carp
•
•
•
•
•
Low
—
—
•
•
•
High
Med
—
ISSUE
HYDRO POWER GENERATION
Effects of possible operating regimes
on value of generation
Privatisation of Southern Hydro —
effects on operation of Dartmouth
Generation at particular times:
• using entitlement water
• when Dartmouth is “above target”
•
Low
—
—
•
Low
—
—
Nil
—
—
Implications of Hume power station on
pulsed releases
•
RECREATION
Effects on recreation of levels of Lake
Hume at different times of the year
•
Low
Low
Low
Effects on recreation of foreshore
erosion — Lake Hume
•
Low
—
—
Effects on recreation of water quality,
especially temperature
•
•
•
•
•
Med
—
Med
Effects of dam operation on recreational
and commercial fishing
•
•
•
•
•
Med - high
—
Med
•
•
•
•
Low (med for —
Yarrawonga
weir pool)
Low–med
Levels of weir pools:
• constancy
• timing of changes
COMMUNICATIONS (really to do with how the review is carried out, not with what is reviewed)
Community participation strategy
during the review
•
•
•
•
•
High
—
High
Is understanding of interested groups
about present operating strategies as
good as it could be?
•
•
•
•
•
High
—
Low
•
•
•
•
•
High
—
Low
•
•
•
•
•
High
—
Low
Disaster planning
•
•
Low
—
—
Dam structural safety
•
•
•
•
•
Low
—
—
Coordinated operation between
Dartmouth/ Hume and the
Snowy Scheme
•
•
•
•
•
Med
—
Med
Yorta Yorta claim
•
•
•
•
•
Low
—
Low–med
Restriction on levels at Lake Victoria
•
•
•
•
•
Med
—
Med
Legal issues, especially liability for
environmental releases that adversely
affect some downstream landholders
•
•
Med
—
Med
Interaction with other current
processes, e.g.:
• Interstate Working Group on
River Murray Flows
• Victorian bulk entitlements
• NSW river flow objectives
Long-term communications between
operators and the interested community
OTHER
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Appendix F: Supporting documents
and references
Support papers
Other sources of information
• All computer runs in tabulated form
I.D & A Pty. Ltd, 1997. Murray River — Hume Dam to
Lake Mulwala River Channel Changes Supplementary Study
— Final Report. Report to the MDBC.
• Detailed description of the parameters of each run
• Submissions made by interested parties
• Set of “Backgrounder” documents
• Investigation of Mitta Mitta flood duration
Reports produced for review
Australian Research Centre for Water in Society.
Operations Review, Hume and Dartmouth Dams — Scoping
Study.
Hassall & Associates. Flood Damage Estimates — A study
of the Murray River and the Mitta Mitta River.
Department of Land and Water Conservation, Murray
Region, Groundwater study — Old Barnawatha.
Chatterton L.A. and Dyson R.K. 1978. Dartmouth Dam
Environment Study, State Rivers and Water Supply
Commission, Melbourne.
Pak Poy and Kneebone, 1988. Hume and Dartmouth
Reservoirs economic study: tourism and recreation studies.
Prepared for the MDBC.
Goulburn-Murray Water 1998, The effects of Dartmouth
Dam on pasture productivity, Mitta Mitta valley — project report.
Murray-Darling Basin Agreement 1992.
Murray Scientific Panel on Environmental Flows 1998,
River Murray — Dartmouth to Wellington and the lower
Darling River.
Dartmouth Power Station — water aspects of the
operating agreement.
Murray Water Entitlement Committee 1997,
Sharing the Murray.
Snowy Water Inquiry 1998, Issues paper.
Snowy Water Inquiry 1998, Final report.
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Glossary
anabranch
A minor (or in some cases below Hume, quite major) stream that leaves and
rejoins the main river.
armouring (of river bed)
Deepening of a river bed can result in the formation of a veneer of gravel on
the bed surface. This “armour” layer is produced by the selective removal of the
finer particles from the bed sediment, and is coarser and better sorted than the
underlying bed material. It is generally only a single grain thick, but quite static
and stable.
bed degradation, bed aggradation
Bed degradation is the deepening of a river channel by erosion. This often
occurs below water storages because the storage traps sediment, increasing the
capacity of the river downstream to mobilise fresh sediment. Aggradation is the
reverse process, where the capacity of the river to transport sediment is reduced
by such factors as lower grade and therefore lower velocity, sediment is
deposited and the stream bed level rises over time.
biota
All living things, including micro-organisms, plants and animals.
bulk water entitlement
A legal document used in Victoria to formally specify the limits to the water
that water authorities may take from a waterway to supply their customers.
cap
The limit placed on taking water from streams in the Murray-Darling Basin for
consumptive use, as determined by the Murray-Darling Basin Ministerial
Council.
channel, river channel
The part of the river where water usually flows; it includes the bed and the
lower part of the banks.
de-snagging
The removal of logs, fallen trees and branches which play an important role in
influencing channel capacity, flow patterns in the river, and riverbed formation.
Snags also provide habitat for instream biota.
DLWC
Department of Land and Water Conservation, New South Wales.
dissolved oxygen (DO)
Water in a healthy stream has oxygen dissolved in it. Low levels of DO indicate
a problem, and may kill fish and other instream biota.
easement
A legal right to do something on someone else’s land. For example it would be
possible for a “flood easement” to be taken out over a part of a property
authorising a storage operator to deliberately flood the land in some months of
the year. A sum of money would normally be payable in exchange for the
acquisition of such a right.
fill and spill
Operating a storage in a simple fashion, making no releases for flood mitigation
but simply allowing the storage to fill, and then to generally pass inflows by
spilling, until it starts to be drawn down by releases for regulated supply.
flood mitigation
Generally, any action that reduces or mitigates floods. Can be applied to storage
operation when it is varied for the purpose of reducing floods. Storages with
free overfall spillways will mitigate floods without specific action by the storage
operator.
floodplain
Land alongside a waterway, which is subject to flooding.
flow regime, river flow regime
The prevailing system of stability within the river channel.
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H U M E A N D D A R T M O U T H D A M S O P E R AT I O N S R E V I E W R E F E R E N C E P A N E L
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HUME AND DARTMOUTH DAMS OPERATIONS REVIEW REFERENCE PANEL